TRNG I HC CN TH KHOA THY SN

GIO TRNH

K THUT SN XUT GING V NUI GIP XC

Ts. NGUYN THANH PHNG Ts. TRN NGC HI

2009

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THNG TIN V TC GI PHM VI V I TNG S DNG

CA GIO TRNH

1. THNG TIN V TC GI H v tn: Nguyn Thanh Phng

Sinh nm: 1965

C quan cng tc:

Khoa: Thy Sn

Trng: i hc Cn Th

a ch Email lin h: ntphuong@ctu.edu.vn

H v tn: TRN NGC HI Sinh nm: 1969

C quan cng tc:

B mn:K Thut Nui Hi Sn, Khoa: Thy Sn

Trng: i hc Cn Th

a ch Email lin h: tnhai@ctu.edu.vn

2. PHM VI V I TNG S DNG

- Gio trnh c th dng tham kho cho nhng ngnh no: Ngnh Nui trng thy

sn, Ngnh Bnh hc thy sn, Ngnh Nng hc

- C th dng cho cc trng no: Cc Trng i hc, Cao ng

- Cc t kha ( ngh cung cp 10 t kha tra cu): Tm bin, tm s,tm th,

cua bin, tm cng xanh, gip xc

- Yu cu kin thc trc khi hc mn ny: Hc vin nm vng mt s vn

v phn loi, sinh hc cc i tng thy sn, mi trng nc, thc n t nhin

cho tm c.

- xut bn in cha, nu c th Nh xut bn no: Gio trnh lu hnh ni b i

Hc Cn Th. Cha xut bn chnh thc nh xut bn.

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MC LC

BA ......................................................................................................................................0 THNG TIN V TC GI ..............................................................................................1 Chng I: M U ..........................................................................................................7 I. i tng, nhim v v ngha ca mn hc..............................................................7 II. Cc i tng gip xc trong nui trng thy sn ....................................................7 III. Lch s pht trin ca sn xut ging v nui gip xc...........................................8

1. Tm bin .......................................................................................................................8 2. Tm cng xanh............................................................................................................11 3. Cua bin ......................................................................................................................12

IV. Tc ng ca ngh nui gip xc .............................................................................12 V. Xu hng nui gip xc hin nay v trong thi gian ti.........................................13 VI Kt cu mn hc ........................................................................................................13 Chng II: K THUT SN XUT GING V NUI TM BIN ......................14 I. c im sinh hc ca tm bin..................................................................................14

1. c im phn loi, hnh thi v phn b tm bin (tm he).....................................14 a. Tm s (P. monodon): .............................................................................................14 b.Tm th ui (P. indicus): ...................................................................................14 c.Tm th ui xanh (P. merguiensis):........................................................................14 d.Tm th chn trng (P. vannamae): ..........................................................................14 e.Tm th Trung quc (P. chinensis hay P. orientalis):...............................................14 f.Tm s Nht bn (P. japonicus): ...............................................................................14 g.Tm t (Metapenaeus ensis): ..................................................................................15

2. Vng i ca tm bin................................................................................................16 3. c im sinh hc sinh sn ca tm bin...................................................................19

3.1. Phn bit tm c v ci.......................................................................................19 3.2. Kch c v tui thnh thc...................................................................................19 3.3. c im giao v ca tm .....................................................................................20 3.4. Pht trin ca tuyn sinh dc ................................................................................21 3.5. trng v sc sinh sn.......................................................................................22 3.6. S th tinh v pht trin phi ...............................................................................23 3.7. Pht trin ca u trng ..........................................................................................23 3.8. S pht trin ca hu u trng ..............................................................................24 3.9. Lt xc v tng trng ca tm...........................................................................24 3.10. Tp tnh bt mi v nhu cu dinh dng............................................................26 3.11. Yu cu mi trng sng....................................................................................28

II. K Thut sn xut ging tm bin ............................................................................29 1. Nc bin....................................................................................................................29 2. Ngun tm b m .......................................................................................................29 3. Nng lng .................................................................................................................30 4. Nc ngt ...................................................................................................................30 5. Hot ng nui tm ....................................................................................................30 6. iu kin thi tit, kh hu v a th.........................................................................30 7. Khong cch gia cc tri ging.................................................................................30 8. Thit k tri ging.......................................................................................................30

8.1. Cc qui m tri ging ..........................................................................................30

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8.2. Trang thit b tri ging ........................................................................................31 9. Nui v tm b m .....................................................................................................33

9.1. Ngun tm b m .................................................................................................33 9.2. Th nui ................................................................................................................34 9.3. Ct mt ..................................................................................................................34 9.4. Qun l mi trng nui tm b m ....................................................................35 9.5. Thc n v cch cho n.........................................................................................36 9.6. Cho v cho n trng.........................................................................................36

10. ng nui u trng...................................................................................................36 10.1. ng nui u trng trong h thng b nh (m hnh Galveston) ......................36 10.2. ng nui u trng theo h thng tun hon .....................................................38 10.3. ng nui u trng trong h thng b ln .........................................................38

11. Vn chuyn v thun ha tm ..................................................................................39 11.1. Vn chuyn v thun ha tm b m .................................................................39 11.2. Vn chuyn v thun ha u trng .....................................................................39 11.3 Vn chuyn v thun ha tm Postlarvae............................................................39

12. nh gi cht lng tm sinh sn.............................................................................40 13. ng tm postlarvae ln ging ................................................................................40

13.1. Ao ng ..............................................................................................................40 13.2. Chun b ao ng................................................................................................40 13.3. Mt th, t l sng v tng trng ca tm ...................................................41 13.4. Cho n, chm sc................................................................................................41 13.5. Thu hoch tm ....................................................................................................41

III. K Thut Nui Tm Thng Phm ........................................................................41 1. c tnh k thut ca cc m hnh nui tm bin .....................................................41

1.1. Nui qung canh (Extensive culture) ...................................................................41 1.2. Qung canh ci tin (Improved extensive culture)...............................................42 1.3. Nui bn thm canh (BTC) (Semi-intensive culture)...........................................42 1.4. Nui thm canh (TC) (Intensive culture) .............................................................42

2. Xy dng ao nui tm (farm design and construction) ..............................................43 2.1. Chn la a im nui (site selection) ................................................................43 2.2. Thit k v xy dng h thng nui .....................................................................45 2.3. Vn hnh tri nui (farm operation) .....................................................................50

3. M hnh nui tm lun canh vi trng la .................................................................67 3.1. Vai tr v tim nng pht trin ca m hnh nui tm nc l lun canh vi trng la.................................................................................................................................67 3.2. K thut nui tm-la...........................................................................................67

4. M hnh nui tm - rng.............................................................................................74 4.1 Tng quan v rng ngp mn v m hnh tm rng .............................................74 4.2. Thit k v xy dng m hnh tm - rng ............................................................75 3.3. Trng rng v chm sc rng trong vung tm...................................................77 3.4. Chun b vung nui.............................................................................................77 3.5. Chn ging tm ....................................................................................................78 3.6. ng tm ging....................................................................................................78 3.7. Th ging nui......................................................................................................79 3.8. Chm sc, qun l.................................................................................................79 4.9. Thu hoch .............................................................................................................81

CU HI N TP CHNG 2....................................................................................83

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Chng III: K THUT SN XUT GING & NUI TM CNG XANH ........84 I. c im sinh hc ca tm cng xanh........................................................................84

1. Phn loi v hnh thi..................................................................................................84 2. Phn b .......................................................................................................................84 3. Vng i ca tm cng xanh ......................................................................................85 4. c im sinh sn .......................................................................................................85

4.1. Phn bit tm c v tm ci ...............................................................................85 4.2. Thnh thc, giao v , trng v p trng ca tm..............................................86 4.3. Pht trin phi.......................................................................................................88 4.4 Pht trin ca u trng ...........................................................................................88 4.5. Pht trin hu u trng..........................................................................................89

5. c im sinh trng..................................................................................................90 6. Yu cu v mi trng sng.......................................................................................91

a) Nhit ...................................................................................................................91 b) mn ....................................................................................................................91 c) Oxy ..........................................................................................................................91 d) m .........................................................................................................................91 e) pH ............................................................................................................................91 f) cng....................................................................................................................91

7. Nhu cu dinh dng ca tm......................................................................................91 a) Cht m..................................................................................................................91 b) Cht bo...................................................................................................................91 c) Cht bt ng ........................................................................................................92 d) Vitamin v cht khong...........................................................................................92

II. Sn xut ging tm cng xanh ...................................................................................92 1. Xy dng tri v chun b tri ging ..........................................................................92

1.1 Chn v tr ..............................................................................................................92 1.2. Thit k, xy dng v phng tin tri ging.....................................................92 1.3. V sinh b, dng c v x l nc ng nui......................................................96

2.Nui tm b m ...........................................................................................................97 3. ng nui u trng.....................................................................................................99

3.1. Cc h thng sn xut ging tm cng xanh ........................................................99 3.2. Cho tm n .........................................................................................................102 3.3. Thu v b tr u trng vo b ng ..................................................................103 3.4. Ch chm sc - cho n ...................................................................................104 3.5. Qun l mi trng nc ng u trng............................................................106 3.6. Chm sc b ng trong giai on chuyn sang tm bt...................................109

4. ng tm ging........................................................................................................111 4.1. Chun b ao, b ng..........................................................................................111 4.2. Chn v th tm bt............................................................................................111 4.3. Chm sc - qun l .............................................................................................111 4.4. Vn chuyn tm bt v tm ging......................................................................112

III. K thut nui tm cng xanh .................................................................................112 1. Cc m hnh nui tm cng xanh .............................................................................112 2. K thut nui tm trn rung la..............................................................................114

2.1. nh ngha cc m hnh nui..............................................................................114 2.2. K thut nui ......................................................................................................115

3. Nui tm cng xanh trong ao....................................................................................117

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a) Chn la a im..................................................................................................117 b) Xy dng cng trnh..............................................................................................119 c) Chun b ao ............................................................................................................121 d) Th ging...............................................................................................................122 e) Cho n v qun l cho n.......................................................................................124 f) Qun l cht lng mi trng ao nui .................................................................125 g) Thu hoch ..............................................................................................................126

4. Nui ng Qung Trn Sng ...................................................................................127 4.1. Chn a im v thit k qung ........................................................................127 4.2. Ci to nn y v chun b ng qung ............................................................127 4.3. Ma v th ..........................................................................................................128 4.4. Chn v th ging...............................................................................................129 4.5. Chm sc v qun l...........................................................................................130 4.6. Thu hoch ...........................................................................................................131

CU HI N TP CHNG 3..................................................................................131 Chng IV: K THUT SN XUT GING V NUI CUA BIN....................132 I. Hnh thi cu to v phn loi ..................................................................................132 II. c im Sinh Hc Sinh Sn Ca Cua Bin....................................................133

1.Vng i ca cua bin ...............................................................................................133 2. Phn bit c ci.......................................................................................................133 3. S thnh thc ca cua bin .......................................................................................133 4. Di c sinh sn............................................................................................................134 5. Tp tnh bt cp, trng v p trng......................................................................135 6. Pht trin ca cc giai on u trng ........................................................................135 7. Kh nng chu ng cc yu t mi trng ca cua bin.........................................136 8. Tp tnh sng ............................................................................................................137 9. Tp tnh bt mi ........................................................................................................137 10. Cm gic, vn ng v t v...................................................................................138 11. Lt xc v ti sinh...................................................................................................138 12. Sinh trng ca cua ................................................................................................138

III. Sinh sn nhn to cua bin .....................................................................................138 1. Nui v cua b m v chm sc cua mang trng .....................................................138

1.1. H thng nui .....................................................................................................138 1.2. Nui v cua b m .............................................................................................138 1.3. Chm sc cua ci mang trng.............................................................................139

2. ng u trng cua ....................................................................................................140 2.1. B ng...............................................................................................................140 2.2. Mt ng........................................................................................................140 2.3. Ch cho n .....................................................................................................140 2.4. Qun l mi trng ng ...................................................................................141 2.5. Nhng tr ngi trong ng u trng cua ............................................................143

3. Nui cua con ............................................................................................................143 IV. K thut nui cua thng phm ............................................................................143

1. Nui cua con thnh cua tht ......................................................................................143 1.1. Ao m nui .......................................................................................................143 1.2. Th ging v chm sc .......................................................................................144 1.3. Thu hoch ...........................................................................................................145

2. Nui cua p thnh cua chc ......................................................................................145

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3. Nui cua gch ...........................................................................................................145 3.1. Phng tin nui.................................................................................................145 3.2. Th ging v chm sc .......................................................................................145 3.3. Thu hoch ...........................................................................................................146

4. Nui cua lt...............................................................................................................146 4.1. Ao nui ...............................................................................................................146 4.2. Th ging v chm sc .......................................................................................146 4.3. Thu hoch ...........................................................................................................146

CU HI N TP CHNG 4..................................................................................147 TI LIU THAM KHO CHNH ..............................................................................148

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Chng I: M U

I. i tng, nhim v v ngha ca mn hc K thut sn xut ging v nui gip xc l mn hc chuyn ngnh quan trng ca

ngnh nui trng thy sn. i tng nghin cu ca mn hc ny l nhng loi tm bin, cua bin, tm cng xanh, tm hm, vn l nhng i tng kinh t quan trng trong sn xut hin nay.

Mn hc nhm gii thiu v cc c im sinh hc sinh sn, k thut sn xut ging nhn to v k thut nui ca cc loi tm, cua. Vi ni dung ca mn hc, sinh vin s c trang b khi kin thc rng v su c th ng dng vo thc t sn xut sau ny. Tuy nhin, c th hiu r rng v vn dng c th vo sn xut, sinh vin cn c thc tp hay kin tp v i thc t sau khi hc xong l thuyt.

Ngoi ra, c th thc s nm vng c mn hc, i hi sinh vin phi c nhng kin thc c bn v c s hay cc mn chuyn mn lin quan nh nui thc n t nhin, thit b v cng trnh thy sn, qun l cht lng nc, bnh hc thy sn, ng loi hc,...

Mn hc c kt cu theo tng chng cho nhng i tng ring, song, nhng chng ny c nhng lin quan vi nhau. II. Cc i tng gip xc trong nui trng thy sn

Mc d, khng phong ph bng c nc ngt hay c nc l, tuy nhin, nhm gip xc cng c kh nhiu loi c nghin cu v pht trin i tr trong sn xut ging v trong nui thng phm. Ty tng vng a l khc nhau cng nh s phn b t nhin ca chng m thnh phn loi gip xc c chn cho nui trng tng vng cng khc nhau. Nhn chung, thnh phn loi gip xc nui vng nhit i phong ph hn vng nhit i v n i; thnh phn loi gip xc nui vng nc l phong ph hn vng nc ngt. Tuy nhin, cc loi tm s, tm th chn trng vn chim sn lng ch yu trong tng sn lng nui. Trong s cc loi gip xc, tm bin (Penaeus spp) v cua bin (Scylla spp) c xu hng pht trin mnh trong thi gian ti (Hambrey, 1999) (Bng 1.1).

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Bng 1.1: Nhng i tng gip xc chnh trong nui trng thy sn Vng a l Nc l, mn Nc ngt Vng nhit i Penaeus indicus Macrobrachium spp. Penaeus merguiensis Chera quadricarinatus P. monodon P. stylirostris P. vannamei Metapenaeus spp. Parulirus spp. Scylla serrata S. olivecea S. paramamosain S. tranqueparica Vng nhit i P. chinensis C. destructor P. japonicus C. tenuimarus P. penicillatus Panilirus spp. Portunus spp. Vng n i Homarus gammarus Astacus leptodactylus H. amaricanus

III. Lch s pht trin ca sn xut ging v nui gip xc Ngh nui trng thy sn ni chung v nui gip xc ni ring t lu da ch yu vo ngun ging t nhin bng cch thu ging vo ao m khi ly nc hay c th nh bt thu gom tm c bt, tm c ging trn cc sng rch, bi bin v th trc tip vo ao m nui. Song, do yu cu pht trin ca ngh nui thy sn, nhng nghin cu sn xut ging v nui c thc hin v gp phn quan trng thc y s pht trin c ngh sn xut ging v nui. 1. Tm bin i vi tm bin, mt trong nhng nghin cu u tin quan trng nht l nghin cu trong lnh vc sn xut ging do Hudinaga Nht Bn thc hin thnh cng trn i tng tm Penaeus japonicus nm 1933 vi qui m b ln. Nm 1966, Cook v Murphy thnh cng trong sn xut ging nhn to tm P. aztecus v P. setiferus vi m hnh Galveston Texas (M). Trong thp k 60-70, m hnh Galveston c ng dng rng ri Chu vi cc loi tm P. indicus, P. merguiensis, P. monodon v P. orientus. Trong thp k 80, m hnh tun hon cng c nghin cu ng dng thnh cng trong sn xut ging tm bin Tahiti v Polynesia (Php). Nu nh trong nhng thp k 60, ngh sn xut ging tm cn da hon ton vo ngun tm m t nhin bt t bin, th thp k 70-80, ngun tm m nui v t ao m c s dng ph bin cho sn xut ging. Chng trnh sn xut tm ging sch bnh v gia ho tm bin cng c bt u Php t 1987 trn i tng P. stiliferus, M t 1989 trn i tng P. vannamae, v c t 1995 trn P. japonicus v 1999 trn P. monodon. n nay, c 24 loi tm thuc ging Penaeus v 7 loi thuc Metapenaeus c nghin cu sinh sn nhn to, trong , c 11 loi c ng dng sn xut ging i tr. i vi nui tm tht, ngh nui tm c bt u t cc nc ng Nam vi hnh thc qung canh. Tuy nhin, ngh nui tm ch tht s bt u pht trin mnh t nhng thp nin 1970. Nm 1975, Ecuador tr thnh nc dn u th gii v sn lng

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tm nui Ty Bn Cu v i Loan, Trung Quc dn u ng Bn Cu. Sn lng tm nui trn th gii tng t 50.000 tn vo nm 1975 ln 200.000 tn vo nm 1985, trong , khong 70% sn lng tm nui n t cc quc gia Chu . Nm 1988, sn lng tm nui trn th gii t 450.000 tn. Tuy nhin, ngh nui tm trong nhng nm ny bt u gp tr ngi ln v bnh tt. i Loan b thit hi nng nht vi sn lng gim t 100.000 tn/nm cn 20000 tn/nm. Nm 1992, Thi Lan tr thnh nc c sn lng tm ng u th gii v tip tc duy tr n gia thp nin 90. Qu trnh thm canh ha trong nui tm Thi Lan tng rt nhanh. Nm 1985, c 94,9 % s ao nui tm l qung canh v ch c 5,1 % s ao nui bn thm canh hay thm canh. Tuy nhin, nm 1995, c n 78,5 % s ao nui thm canh, 7 % nui bn thm canh v 14,5% nui qung canh. Nng sut tm cng khng ngng gia tng t 456 kg/ha/nm vo nm 1985 ln 2.325 kg/ha/nm vo 1990 v 3.850 kg/ha/nm vo 1995. Trung Quc, qu trnh nui tm bin Trung Quc tri qua 4 giai on chnh l giai on tng trng cht (1978-1984), giai on tng trng nhanh (1984-1988), giai on y trin vng (1988-1992) v giai on suy thoi (1993-1994). Nm 1993-1994, ngh nui tm Trung Quc b sp do dch bnh, sn lng gim t 200.000 tn (1992) xung cn 50.000 tn nm 1993.

T nm 1995, ngh nui tm trn th gii tng trng chm li do dch bnh virus xy ra trn ton cu. D th, sn lng vn tng do nhiu cng ngh mi c p dng. Theo thng k ca FAO (1998), sn lng tm nui ton cu nm 1996 t 900.000 tn. Chu l ni nui tm ch yu, chim 84 % sn lng tm nui mi nm. Theo Ruampron (...), nhng l do chnh dn n s pht trin nhanh chng ca ngh nui tm Chu l do s pht trin mnh m trong k thut sn xut ging tm s khi xng i Loan t nhng nm 1970; c din tch mt nc l thun li cho ngh nui tm; v s pht trin k thut nhanh chng t hnh thc nui qung canh sang qung canh ci tin v thm canh. Trong s cc loi tm nui, tm s l quan trng nht v c nui rng ri nht. Thng k ca FAO (2002), sn lng tm s, tm th chn trng v tm he Trung Quc chim sn lng cao nht (Hnh 1.1)

Hnh 1.1. Sn lng tm nui trn th gii (FAO, 2001)

Vit nam, nghin cu sinh sn nhn to tm bin u tin c tin hnh Min Bc t nhng nm u thp k 70 vi cc loi tm P. merguiensis, P. penicilatus v P.

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japonicus. Nm 1982, tri sn xut ging tm bin i tr c thnh lp Qui Nhn do FAO h tr. T 1985, tm s c sinh sn nhn to thnh cng Nha Trang v dn tr thnh i tng ch yu trong sn xut ging v nui tm bin nc ta. Nm 2000, tm th chn trng ln u tin c nhp vo nc ta nui th nghim ti Bc Liu, sau , c sn xut ging v nui mt s tnh khc trong nc. Nghin cu sn xut ging ln u tin c tin hnh vo nm 1987-1988 trn i tng tm th. Sau , cc tri sn sut ging i tr bt u c thnh lp v c pht trin nhanh chng. Nm 1994, c nc c 800 tri sn xut ging. Nm 1999, trn c nc c 2125 tri tm (B Thy sn, 1999), v 2002 c 4774 tri (B Thy sn 2003). Khu vc sn xut tm ging tp trung nht nc ta l cc tnh Khnh Ho, Ninh Thun v C Mau vi s tri tng ng l 1260 tri, 1169 tri v 821 tri vo nm 2002. Sn lng tm Postlarvae sn xut nm 2002 ca c nc t trn 19 t con. Bng 1.2: Pht trin v din tch v sn lng tm s nui Vit Nam v BSCL

Vit Nam BSCL Nm Din tch (ha) Sn lng (t) Din tch (ha) Sn lng (t)

1991 222.000 35.600 - - 1994 253.000 65.600 - - 1999 203.323 65.282 173.510 49.624 2000 259.688 103.845 265.261 72.305 2001 449.275 162.713 404.911 143.822 2002 478.785 193.973 417.398 153.122 2003 546.757 200.000 463.889 169.000

Bng 1.3: Pht trin v tri ging, sn lng ging sn xut v ging nhp ca BSCL Vit Nam BSCL Nm

Trai ging Sn lng PL sn xut (triu)

Tri ging Sn lng PL sn xut (triu)

Sn lng PL nhp (triu)

1986 16 3.3 - - - 1990 215 250 - - - 1995 675 2.300 - - - 1997 - - 134 218 1.703 1998 1.489 4.685 350 701 4.001 1999 2.116 7.466 416 1.219 6.001 2000 2.763 10.271 465 1.340 6.500 2001 4.071 16.247 550 2.500 12.000 2002 4.774 19.088 1.003 3.877 15.000 2003 5.017 25.008 1.089 7.963 _?

i vi ngh nui tm tht, ngh nui tm nc ta cng pht trin vi nhiu giai

on khc nhau t hnh thc qung canh t nhng nng 1970, qung canh ci tin t nhng nm 1980, bn thm canh v thm canh t 1990 n nay. Ngoi ra, cn c nhiu m hnh kt hp rt trin vng nh m hnh tm-rng, tm-la Theo bo co ca B Thy sn (1999), nm 1944, c nc nui 230.000ha tm bin t sn lng 56.000 tn, v tng ln 295.000 ha v 70.000 tn nm 1998. Nm 2003, din tch nui tm tng n 546.757 ha v t sn lng l xp x 200.000 tn, ng bng Sng Cu Long c tng cng 450.000 ha vi hn 170.000 tn (B Thu sn, 2004). Nhn chung, m hnh nui tm bn thm canh v thm canh hin ang pht trin nhanh chng, m hnh nui

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tm qung canh ci tin (k c nui n, tm rng hay tm-la) hin vn chim a s v din tch v sn lng tm nui.

0

10

20

30

40

50

60

70

80

Qung canh QC ci tin Bn thm canh Thm canh

Cc m hnh nui

T l

%

Nm 2002

Nm 2003

Hnh 1.2 Pht trin ca cc m hnh nui tm Vit Nam (B Thu sn 2003 v 2004)

2. Tm cng xanh

Tm cng xanh l cng l i tng gip xc quan trng trong nui trng thy sn. Tm c ngun gc vng n -Thi Bnh Dng, tuy nhin, hin nay, tm c di nhp sang nhiu nc trn th gii.

Lch s pht trin ca ngh nui tm cng xanh c bt u t nm 1962 khi Ling ln u tin thnh cng trong vic ng nui u trng v m t cc giai on u trng. Qui trnh sn xut ging tm cng xanh theo h thng nc trong h t cng c xy dng. Qui trnh ny c AQUACOP hon thin t nm 1977. Nm 1966, Fujimura thnh cng trong vic sn xut ging i tr tm cng xanh Hawaii theo m hnh nc xanh vi ngun tm b m nhp t Malaysia. Trong sn xut ging tm cng xanh, c mt s qui trnh khc c nghin cu v ng dng rng ri hin nay l qui trnh nc trong - tun hon do mt s tc gi nh Sandifer (1977), Menasveta (1980), Singholka (1980) nghin cu v c cn bn hon chnh a vo sn xut i tr nm 1984; qui trnh nc xanh ci tin c Ang xng t nm 1986 trn c s ci tin m hnh nc xanh trc .

Trong nui tm tht, s liu ghi nhn u tin cho thy, nm 1984, sn lng tm cng xanh nui trn th gii t 5.246 tn. Nm 1989 t 17.608 tn. Tng sn lng tm cng xanh trn th gii t trn 119.000 tn vo nm 2000. Chu l ni c sn lng tm cng xanh ln nht, chim 94% tng sn lng tm trn th gii (FAO, 2002). Nm 2003, ch ring Trung Quc sn xut 300.000 tn tm cng xanh (Miao, 2003).

nc ta, ngh nui tm cng xanh l ngh truyn thng bng cch nui nh, c bit l vng BSCL. Vic nghin cu sn xut ging tm cng xanh c bt u t nhng nm u thp nin 80 vi qui trnh nc trong h v tun hon. Tuy nhin, sn xut ging tm cng xanh nhn to ch pht trin mnh t 1999 khi nhu cu con ging ngy cng cao v thnh cng trong vic nghin cu v ng dng m hnh mi l m hnh nc xanh ci tin. BSCL t ch mt vi tri tm cng xanh vo nm 1999, n 2003, c 91 tri, t sn lng 76 triu tm bt/nm.

Trong nui tm tht, nm 2002, c nc t 10.000 tn (B Thy sn, 2003), ch yu t cc tnh BSCL. Cc m hnh nui tm vi nhiu hnh thc khc nhau nh nui

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tm kt hp vi la t nng sut bnh qun 184kg/ha/v; nui tm lun canh vi la t 686 kg/ha/v, nui ao t 1,2 tn/ha/v v nui tm ng qung trn sng t bnh qun 4,12 tn/ha/v (Phng, 2003).

0

10

20

30

40

50

60

70

80

90

100

1999 2000 2001 2002 2003

S tri

/ s

n l

ng

Tri gingSn lng PL (tr. con)

Hnh 1.3. Pht trin tri ging v sn lng tm cng xanh Vit Nam t nm 1999-2003 (Ngun: Hi v ctv. 2003)

3. Cua bin Cua bin l i tng gip xc quan trng trong nui trngv khai thc thy sn. C 4 loi cua bin c nh danh l Scylla serrata, S. paramamosain, S. olivacea, S. transqueparica. Vit Nam c 2 loi l S. paramamosain, S. olivacea. Trong nghin cu sn xut ging cua bin, nm 1964-1966, Ong kah Sin ln u tin thnh cng trong vic nghin cu ng u trng v nui cua tht v khp kn vng i ca cua. T , lm c s cho nhiu nghin cu khc cc ni. Tuy nhin, n nay, vic sn xut ging cua bin i tr cho ngh nui cc nc vn cn kh khim tn m ch yu l qui m thc nghim. Ngh nui cua bin v th vn cn da ch yu vo ngun cua ging bt t t nhin cc ca sng, rng ngp mn, bi triu ven bin. Cc m hnh nui cua bin kh a dng nh nui cua con thnh cua tht, nui cua gch, nui p thnh cua cht v nui cua lt. C th nui trong ao hay trong lng. Theo FAO, tng sn lng cua bin nui cc nc hng nm trong giai on 1984-1997 dao ng trong khong 5.000-10.000 tn/nm. Cc nc c ngh nui cua ph bin nh Philippines, Indonesia, i Loan, Thi Lan, Vit Nam. Sn lng cua bin nui Vit Nam nm 2002 t 13.000 tn. BSCL, m hnh nui cua con thnh cua tht kt hp vi nui tm trong rng ngp mn rt ph bin vi nng sut trung bnh 50-100 kg/ha/nm. Bn cnh nhng i tng trn, cn nhiu i tng gip xc khc ang c pht trin nui nh tm hm, tm m ni, gh xanh, Artemia. IV. Tc ng ca ngh nui gip xc Ngh nui gip xc m quan trng nht l ngh nui tm bin mc d v ang gp phn rt quan trng trong ci thin i sng ngi dn, to cng vic lm, to sn phm c gi tr cao v c th trng rng cho x hi. Tuy nhin, ngh nui cng c th gy ra nhiu tc ng tiu cc ln mi trng v kinh t x hi

- Tc ng ln mi trng - nhim do cht thi giu dinh dng t ao nui - nhim t ha cht s dng trong nui thy sn

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- Cn kit nc ngm - Mn ha t v nc - Tn ph rng ngp mn - Suy gim sn lng v tnh a dng sinh hc ngun li thy sn - Di nhp cc loi nui l nh hng n qun th a phng

- Tc ng n kinh t x hi - Mu thun gia cc thnh phn kinh t - Thay i quan h v phn cp x hi - Tht nghip v di dn - An ton lng thc b e da

V. Xu hng nui gip xc hin nay v trong thi gian ti Trong ngh nui gip xc, cho n nay, tm bin lun l i tng quan trng v c nui ph bin nht. Tuy nhin, ngh nui tm bin tri qua nhng giai on rt c th:

- Giai on thp nin 60-80: Giai on ny ch yu l nghin cu v pht trin k thut v qui m nui trng, m tip theo , ngh nui pht trin rt nhanh chng.

- Giai on thp nin 80-90: Giai on ny c nhiu tr ngi xy ra lin quan n bnh tt, suy thoi ti nguyn, nhim mi trng, mu thun v kinh t x hi.

- Giai on hin nay v tng lai: Do nhng tr ngi trn, xu hng hin nay v trong thi gian ti l nui tm theo hng bn vng vi s a dng ha i tng nui, ci thin qui hoch v qun l trong pht trin nui trng.

VI Kt cu mn hc Mn hc s c chia thnh 4 chng ging dy, trong mi chng sinh vin s c ging dy v sinh hc ca i tng nui v k thut sn xut ging v nui thng phm. V phn k thut, ngoi vic ging dy cc nguyn l chung, bi ging s cp nhiu n cc gii php k thut ang c vn dng iu kin Vit Nam sinh vin thy gn gi v khi ra trng c th vn dng ngay. Cc chng hc c th l: Chng 1: M u Chng 2: Sinh hc v k thut nui tm bin Chng 3: Sinh hc v k thut nui tm tm cng xanh Chng 2: Sinh hc v k thut nui cua bin

13 i

Chng II: K THUT SN XUT GING V NUI TM BIN

I. c im sinh hc ca tm bin 1. c im phn loi, hnh thi v phn b tm bin (tm he)

Cc loi tm he thuc h thng phn loi sau: Ngnh: Arthropoda Ngnh ph: Crustacea Lp: Malacostraca B: Decapoda Ging: Penaeus Metapenaeus

Mt s loi tm quan trng trong nui trng thy sn bao gm tm s (P. monodon), tm th ui (P. indicus), tm th ui xanh (P. merguiensis), tm th chn trng (P. vannamei), tm th Trung Quc (P. chinensis), tm th Nht bn (P. japonicus) v tm t (M. ensis).

a. Tm s (P. monodon): chy c 7-8 rng trn chy v 3-4 rng di chy. Chy cong xung rt t. G gan di v cong. Gai ui c rnh nhng khng c gai bn. Phn u ngc v phn bng c nhng bng en ngang. Chn ngc c th c mu . y l loi tm kinh t c kch c ln nht, c th di n 330mm hay hn.

b.Tm th ui (P. indicus): Chy c gc khuu nh cao, c 7-9 rng trn chy v 4-5 rng di chy. Rnh gc chy r rng, gn vi rnh gia, v ko di n gia gip du ngc. G hc mt-d dy r rng nhng g gan ty khng c. Gai ui c hnh tam gic rng v c rnh gia chy dc vi nhiu gai nh mu en. Tm c mu trng kem vi nhng qung xanh. Chn mu v chy mu xanh. Loi ny tng t nh tm th ui xanh v giai on tm ging ca hai loi rt kh phn bit.

c.Tm th ui xanh (P. merguiensis): Chy ko di, ngang, c gc khuu cao, c 6-10 rng trn chy v 6 rng di chy. Rnh gc chy v rnh gia cn, nh dn v gia gip u ngc. Khng c g d dy - hc mt, khng c g gan ty. V y ngc nhn. Tm c mu trng kem.

d.Tm th chn trng (P. vannamae): Chy hi cong xung, c 8-9 rng trn chy v 1-3 rng di chy. C th c mu trng, chn mu trng hay nht nht. Tm ny rt kh phn bit vi loi xanh (P. styliferostris).

e.Tm th Trung quc (P. chinensis hay P. orientalis): Chy c gc khuu thp, nm ngang. C 7-9 rng trn chy v 3-4 rng di chy. Gai ui c hnh tam gic hp, ngn hn chn ui v khng c gai bn. Tm c mu trng kem, chy v gai ui sm hn.

f.Tm s Nht bn (P. japonicus): Gip u ngc nhn, bng, khng c lng t. Chy nm ngang nhng hi cong nh xung, c 8-10 rng trn chy v thng ch c 1 rng di chy. Rnh gc chy v rnh gia ko di n b sau ca gip u ngc. Gai ui c cc gai bn c th c ng. Phn bng c khong 10 hay hn sc ngang mu nu. Phn trn ca gip u ngc, chn v chn ui cng c nhiu sc ngang. Chn c mu ; gai ui v chn ui c mu pha gia , xanh, vng.

14 i

g.Tm t (Metapenaeus ensis): Chy nm ngang v hp, c 8-9 rng trn chy v khng c rng di chy. Gai ui c rnh rng khng c gai. C th c mu nu nht n hng trng. Ru mu hng , chn ui mu v chn mu hng.

Cc loi tm he phn b ch yu vng nhit i v nhit i, t 40o v Bc n 40o v Nam. Vng n -Thi Bnh Dng c thnh phn loi phong ph. Hu ht cc loi tm kinh t quan trng thuc Penaeus c giai on trng thnh vng bin khi (khng su qu 180m) v giai on u nin vng ven b. Ty loi tm khc nhau m chng thch phn b nhng ni c nn y khc nhau. V d, tm th ui thch sng ni c y mm, bn, v nc c. Loi tm ny khng vi mnh, nhng c kh nng lm c nn y bo v khng b k th tn cng. Trong khi , mt s loi sng ni nc trong phi vi mnh xung ct trnh k th.

Hnh 2.1: Tm s (Penaeus monodon)

15 i

Bng 2.1: Phn b ca mt s loi tm kinh t quan trng v tp tnh ca chng Loi Phn b Ni sng

P. monodon Vng n -Ty Thi Bnh Dng: t ng v ng nam Chu Phi, Pakistan n Nht Bn, xung Indonesia v Bc c

Su 0-162m, y bn, hay ct; trng thnh sng bin, u nin sng ca sng.

P. indicus n - Ty Thi Bnh Dng: ng n ng Nam Chu Phi n Trung Quc, Indonesia, New Guinea, bc v ng Bc c.

Su 2-90 m, y bn, hay ct; trng thnh sng bin, u nin sng ca sng.

P. merguiensis n - Ty Thi Bnh Dng: T Vnh Thi Lan n Hongkong, Philippines, Indonesia, New Guinea n Ty, Bc v ng c.

Su 10-45 m, y bn, sng ca sng v bin.

P. japonicus n - Ty Thi Bnh Dng: T Bin , ng v ng Nam Chu Phi n Triu tin, Nht Bn, xung Indonesia, Bc v ng Bc c n Fiji.

Su 0-90 m, y ct hay ct bn, bin.

P. vannamei ng Thi Bnh Dng: T Bc Mexico n Peru.

Su 0-72 m, y bn, trng thnh bin, u nin ca sng.

M. ensis n - Ty Thi Bnh Dng: T Sri Lanka, Malaysia n Trung Quc, Nht bn, xung Indonesia, New Guinea, Ty-Bc ng c

Su 18-64m, y bn, sng bin v ca sng.

2. Vng i ca tm bin

Vng i ca tm bin tri qua mt s giai on bao gm giai on trng; u trng (gm 3 giai on ph: Nauplii, Zoae, v Mysis); hu u trng; u nin v giai on trng thnh. Mi giai on phn b nhng vng khc nhau nh vng ca sng, vng bin ven b hay vng bin khi v c tnh sng tri ni hay sng y. Ty theo tng loi vi nhng tp tnh sng khc nhau m c phn thnh 4 dng chu k sng (Dall v ctv. 1990)

Dng I: Ton b cc giai on trong chu k sng trong vng ca sng. Dng ny bao gm nhng loi c kch c nh thuc ging Metapenaeus nh M. benettae, M. conjuntus v M. moyebi. Mc d, sng ch yu vng nc l ca sng, giai on hu u trng c khuynh hng i ngc dng ln vng nc lt hay c nc ngt sng, tm ln ln s ra vng ca sng sinh sn. y l nhng loi rt rng mui.

Dng II: Chu k sng c giai on hu u trng phn b ch yu vng ca sng. Dng ny c trng cho hu ht cc loi thuc ging Penaeus v Metapenaeus. Mt vi loi ca Parapenaeopsis cng thuc dng ny. Hu u trng thng c tr trong vng rng ngp mn ni mn c th thay i ln. Giai on u nin thng rng mui v cng c tr vng ca sng. Khi gn n giai on thnh thc, tm s ri ca sng di c ra vng bin khi sinh sn. Trng thng c kch c nh (0,27 mm i vi Penaeus) v c tnh chm.

16 i

Dng III: c trng ca dng chu k ny l giai on hu u trng sng ch yu ni c mn cao nh vng bin ven b, c gi th. Dng ny bao gm nhng loi thuc Metapenaeopsis, Parapenaeopsis, mt vi loi thuc Metapenaeus v Penaeus. Cc bi c bin l ni sinh sng l tng ca cc loi ny. Tm trng thnh di c ra bin khi sinh sn. Trng c th l trng ni hay chm.

Dng IV: Ton b cc giai on ca i sng tm vng bin khi. Hu ht cc loi thuc Parapenaeus v Penaeopsis thuc dng ny.

Hnh 2.2: Chu k sng ca tm bin - Dng I

Hnh 2.3: Chu k sng ca tm bin - Dng II

Juvenile Trng thnh trng

Trng

Mysis Zoae

NaupliusPostlarva

Tng mt

Tng y

VNG CA SNG VNG VEN B

Juvenile Trng

Mysis Zoae

Nauplius

Trng thnh trng

Postlarvae

Tng y

VNG CA SNG VNG VEN B VNG KHI

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Hnh 2.4: Chu k sng ca tm bin - Dng III

Juvenile Trng

Mysis Zoae

Nauplius Postlarvae

Trng thnh trng

Trng

Tng y

Tng mt

CA SNG VNG VEN B VNG KHI

Hnh 2.5: Chu k sng ca tm bin - Dng IV

Tng y

Juvenile

Trng

Mysis Zoae

Nauplius Postlarvae

Trng thnh trng

Postlarvae

Juvenile

Tng mt

VEN B VNG KHI

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Hnh 2.6: Vng i tm s (Penaeus monodon)

3. c im sinh hc sinh sn ca tm bin 3.1. Phn bit tm c v ci

Tt c cc loi tm he u c cc c quan sinh dc ph. con c, cc nhnh trong ca chn bng th nht bin thnh c quan giao v (petasma). Khi cha thnh thc, cc nhnh trong ny n thun l nhng nhnh thon, dp, nhng khi thnh thc, chng ko di v dnh li vi nhau nh nhng lng mc nh gia chng. Cu trc ca Petasma c trng ring cho tng loi.

C quan sinh dc trong ca tm c bao gm mt i tinh so, i ng dn tinh v u mt nm vng tim pha trn ca gan ty. Tnh so trong sut v c 5-8 thy lin kt li phn gc v v ng dn (deferens). ng dn gm c on u ngn v hp; on gia dy v ln v on cui di hp. u cui ca ng c ti tinh v ra gc ca chn ngc 5 m c th nhn thy qua lp v. Ti tinh c hnh thnh khi cc tinh trng i qua ng dn.

C quan sinh dc ca tm ci l thelycum. Thelycum l a bin dng ca t ngc th 7 v 8. Ty theo loi m c cu trc thelycum khc nhau. N c th n gin l Thelycum h hay phc tp hn vi Thelycum kn (c 1 hay 2 tm y).

C quan sinh dc trong ca tm ci bao gm mt i bung trng v ng dn trng. Bung trng ko di theo chiu di c th khi tm trng thnh. Bung trng c nhiu thy phn u v nm gn d dy v vng tim. Cc thy bn nm pha trn ca gan ty. Thy bng nm gia mt bn v trn ca dy rut v pha di ca cc mch mu bng trn lng.

3.2. Kch c v tui thnh thc Motoh (1981) cho rng, tm t thnh thc l lc kch c nh nht m c th thy

ti tinh u c quan giao v ca con c v trong ti cha tinh con ci. Trong t nhin, cc loi tm thuc ging Penaeus thng t tui thnh thc sau 8-10 thng. tui ny, tm c th t 40 g i vi P. vannamei hay P. stylirostris. Tm s P. monodon

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l loi c kch c ln, song, chng c th thnh thc kch c 35 g i vi con c v 67,7 g i vi con ci. Trong ao, tm c c th t thnh thc trng lng 20 g v con ci 41,3 g (Motoh, 1981).

3.3. c im giao v ca tm Tm bin c phn loi thnh hai nhm da trn c im sinh dc ci l nhm c

thelycum h v nhm c thelycum kn. c im giao v ca hai nhm ny cng khc nhau. i vi nhm c thelycum h, tm giao v ch vi gi trc khi trng v ti tinh ca tm c c chuyn sang tm ci v nm bn ngoi thelycum th tinh cho trng khi . Trong khi , nhm c thelycum kn, tm ci ch giao v khi va lt xc. Ti tinh ca tm c c chuyn sang ti ca tinh nm trong thelycum ca tm ci. Ti tinh ny s c gi th tinh cho vi ln trng hay n khi tm ci lt v. V th, tm ci c thelycum h tun theo th t: lt xc - thnh thc - giao v - trng, v tm ci c thelycum kn tun theo th t: lt xc - giao v - thnh thc - trng.

Hin tng giao v tm xy ra khi c s tit pheromone sinh dc ca tm ci v tm c nhn bit nh ru th nht hay gai ru th nht.

tm c thelycum kn, giao v xy ra sau khi lt xc ca con ci v vo ban m, khong 22:30-2:00 i vi P. semisulcatus hay 18:00-6:00 i vi P. monodon. i vi tm c thelycum h, giao v xy ra ch yu vo u hm ca m trng, khong 19:00-21:00.

Cc bc trong qu trnh giao v ca tm (c thelycum h v kn) c m t nh sau: (i) mt hay nhiu con c b con ci hp dn, tip cn con ci t pha sau, con c chm u gai chy vo di ui con ci; (ii) Con ci bi ln mt, v chng rt ui nhau hay bi song song, con c thng bi pha di v sau con ci; v (iii) T pha di con ci, con c tr nga ln, u p u, bng p bng vi con ci. mt s loi P. monodon, P. semisulcatus, P. stylirostris..., con c sau quay vung gc vi con ci, bng co u v ui vi ln chuyn ti tinh vo con ci. i vi P. vanamei, P. japonicus, con c v ci giao v vi t th u p u, bng p bng hay u p ui, bng p bng ch khng c hng vung gc.

Hnh 2.7: c im giao v ca tm s (Penaeus monodon) qua cc giai on t (a)(d)

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3.4. Pht trin ca tuyn sinh dc a) Pht trin tuyn sinh dc c Tinh dch c mu sa hay xm nht. Tinh trng khng di ng, c hnh qu cu c

chp gai. Tuy nhin, ty tng loi khc nhau m hnh dng tinh trng v chp gai khc nhau. S lng tinh trng c lin quan n loi v trng lng ca tm. Tm P.setiferus trng lng 35g c th c 70 triu tinh trng. Tinh trng c kch c 5 x 3,1m P. merguiensis, 2-4 x 3,1-8 P. indicus.

b) Pht trin tuyn sinh dc ci tm s (P. monodon), c 5 giai on pht trin ca bung trng da trn s khc

bit v c trng, rng tuyn sinh dc, v mu sc (Villaluz, 1969; Primavera, 1980; Motoh, 1981).

Giai on I Bung trng mng, trong sut, khng nhn thy c t bn ngoi. tm s, giai

on ny trng c kch c 36 m th c bao bi mt lp folicule v trng ln hn s c nhn v ht non hong. giai on thoi ho, trng cng cha non hong v c lp folicule dy, trng c hnh dng khng u.

Giai on II (giai on pht trin) Bung trng mm v c mu trng hay xanh -liu, dng dy thng. Trng c kch

c trung bnh 177 m c nhng ht non hong. T bo c cht nguyn sinh bao gm nhng ht glycoprotein nh, git lipoglycoprotein v git du.

Giai on III (giai on gn chn) Bung trng c mu xanh nht, phn trc dy v n rng. C th thy bung trng

d dng qua lp v, c bit t bng th nht. Trng c kch c trung bnh 215 m. Giai on IV (giai on chn) Bung trng c dng ht kim cng, n rng ph khp t bng th nht. Trng

c mu xanh -liu m hay xanh ru m v ph y khoang c th. Trng c kch c trung bnh 235 m. Tm giai on ny thng c s dng cho sinh sn trong tri ging.

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Hnh 2.8: Cc giai on pht trin ca bung trng tm s (Penaeus monodon)

3.5. trng v sc sinh sn Tm trng vo ban m, thng 22:30-0:30 gi. Tuy nhin, ty tng loi v tng

ma m thi gian trng ca tm cng khc nhau. P. japonicus ch yu t 20:00-0:00 gi vo thng 6-7 v 0:00-4:00 gi vo thng 7-9 dng lch. Tm th P. merguiensis thng trc 22:00. Trong t nhin, tm thng 1 ln trong mi chu k lt xc, song, trong iu kin nui, tm c th nhiu ln (c th n 6 ln).

Trc khi trng, tm ci nm yn trn y b. Khi bt u trng, con ci bi ti v thnh thong bng nhanh. Sau , bi chm li v trng ri vo nc. Cc chn bng hot ng nhanh phn tn trng u trong nc v ri xung y b. i khi, trng khng ri u ra m dnh li thnh m trn y b, iu ny s lm trng b h v khng n c.

Ty theo loi, kch c v tnh trng tm m sc sinh sn ca tm cng khc nhau. Cc loi tm c kch c nh nh Metapenaeus v Parapenaeopsis c sc sinh sn thng 124.000-400.000 trng. i vi nhng loi c kch c ln nh thuc Penaeus, sc sinh sn 100.000-1.000.000 trng. Trong iu kin nui, sc sinh sn ca cc loi thuc Penaeus thng t 50.000-300.000 trng.

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3.6. S th tinh v pht trin phi S th tinh xy ra khi trng va c phng ra. i vi tm ci c thelycum h, ti

tinh dnh bn ngoi thelycum, v th c th c kh nng trng c th tinh khi tip xc vi khi tinh, hoc tinh trng c phng ra cng lc trng v s th tinh din ra trong nc. i vi tm ci c thelycum kn, trng c th tinh ngay khi c phng qua khi tinh. Trng c kch c khc nhau ty tng loi. Trng tm Parapenaeus c kch c ln nht (690-720 um); trng Metapenaeus c kch c trung bnh (trung bnh 342 um) v tip theo l trng Penaeus (trung bnh 276 um). P. japonicus c trng c 260-280 um; P. indicus 270 um, P. merguiensis 270-280 um v P monodon 250-330 um. Nhn chung, ty theo kch c trng m n s c tnh ni, l lng hay chm. Trng ca nhm Penaeus thng c kch c nh nn c tnh l lng hay chm. Sau khi trng v th tinh khong 30-40 pht, mng keo bao trng bin mt, trng c dng cu v s phn chia hp t ln th nht bt u v mt khong 2-3 pht. S phn chia ln th hai din ra 12-14 pht sau . Sau khi 2-2.5 gi, mng phi xut hin bao quanh phi. Trng n 12-14 gi sau khi . Tuy nhin, ty tng loi khc nhau, s pht trin phi cng khc nhau. Bng 2.2: So snh s pht trin phi gia ba loi tm

Thi gian sau khi Giai on trng P. semisulcatus P. monodon P.merguiensis

2 t bo 40 pht 40 pht 40pht4 t bo 1 gi 20 pht 1 gi 50 pht8 t bo 1 gi 30 pht 1 gi 10 pht 1 gi 10 pht16 t bo 1 gi 50 pht 1 gi 25 pht 1 gi 25 pht32 t bo 2 gi 1 gi 35 pht 1 gi 50 pht64 t bo 2 gi 20 pht 1 gi 35 pht 1 gi 55 pht128 t bo 2 gi 40 pht 2 gi 05 pht 2 gi 20 phtRu th 2 4 gi 3 gi 50 pht 4 giRu th nht 7 gi 20 pht 6 gi 50 pht 6 giTrng n 18 gi 15 gi 2 gi

3.7. Pht trin ca u trng

Ngoi tr mt s loi, hu ht cc loi tm bin u tri qua cc giai on u trng tng t nhau vi Nauplius (6 giai on), Zoae (3 giai on) v Mysis (3 giai on).

Nauplius: u trng Nauplius mi n c chiu di khong 0.3mm, c 3 i ph b v mt im mt gia trc. u trng c tp tnh tri ni, hng quang, dinh dng bng non hon.

Zoae: bao gm 3 giai on ph: - u trng Zoea 1: phn bit Zoae1 vi Nauplius qua mt s c im nh c

carapace trn, cc ph b v gai ui pht trin. giai on Zoae2, u trng xut hin 2 mt c cung, chy c rng, bng pht trin di ra. i ru th nht hng ra pha trc.

23 i

- u trng Zoae3 c cc gai lng v gai bng trn cc t bng. Ru th nht to hn v c nhiu lng t. Cc mm chn ngc xut hin pha sau cc ph b ming. c im r nht l chn bng (uropod) xut hin trc ui.

- u trng Zoae c tnh n lc, th ng, thc n chnh l to, c kch c 3-30 um. Tuy nhin Zoae1 vn cn s dng non hon trong khi bt u n ngoi. Zoae c tnh hng quang mnh.

Mysis: c 3 giai on ph, giai on Mysis1 c c th ko di, chn ngc pht trin, telson xut hin, cha c chn bng. Mysis2 c mm chn bng nhng cha phn t. Mysis3 c chn bng pht trin di gp i so vi giai on Mysis2, chn bng c 2 t. u trng Mysis dn dn chuyn sang n ng vt phiu sinh, bi nga v git v pha sau. Bng 2.3: Tui v kch c cc giai on u trng tm s (P. monodon) (Kungvankij v

ctv, 1986) Giai on Chiu di trung bnh

(mm)Thi gian sau khi n

Nauplius 1 0,32 15 giNauplius 2 0,35 20 giNauplius 3 0,39 1 ngy 2 giNauplius 4 0,4 1 ngy 8 giNauplius 5 0,41 1 ngy 14 giNauplius 6 0,54 1 ngy 20 giZoae 1 1,05 2 ngy 16 giZoae 2 1,9 4 ngy 4 giZoae 3 3,2 6 ngyMysis 1 3,8 7 ngy 4 giMysis 2 4,3 8 ngy 16 giMysis 3 4,5 9 ngy 4 giPost larvae 1 5,2 10 ngy 20 giPost larvae 5 8 16 ngyPost larvae 15 12 26 ngyPost larvae 20 18 31 ngy

3.8. S pht trin ca hu u trng

Sau giai on Mysis 3, u trng chuyn sang giai on hu u trng (tm bt - postlarvae) v c hnh dng tng t nh tm trng thnh. Postlarvae u tin c chiu di khong 4,5mm. Cc chn bng c nhiu lng t. Postlarvae giai on u mt s cn tp tnh bi trong ct nc, phn ln bt u sng y. T Postlarvae 6, tm ch yu sng y.

3.9. Lt xc v tng trng ca tm Tm he cng ging nh cc loi gip xc khc, chng ln ln nh lt xc. Tin

trnh lt xc ca tm tri qua mt s giai on chnh l tin lt xc, lt xc, hu lt xc, gia chu k lt xc, vi nhng din bin bao gm (i) s kt dnh gia biu m v v tm b lng lo ra, (ii) c th nhanh chng rt ra khi v c, (iii) c th hp th nc n rng v v ln nhanh; (iv) c th cng cp li nh cht khong v cht m. Do c hin tng lt xc m qu trnh tng trng ca tm khng lin tc m c tnh gin on.

24 i

Qu trnh lt xc ca tm c iu khin nh hormone lt xc c tit ra t c quan Y v hormone c ch lt xc c tit ra t c quan X. Chu k lt xc l thi gian gia hai ln lt xc lin tip nhau, chu k ny mang tnh c trng ring bit cho loi v giai on sinh trng ca tm. Chu k lt xc s ngn giai on tm con v ko di khi tm cng ln. Ngoi ra, qu trnh lt xc v tc tng trng ca tm cn b nh hng rt ln bi rt nhiu yu t nh loi, dinh dng, mi trng nc (Bng 2.4) Bng 2.4: Chu k lt xc ca tm

C tm (g) Chu k lt xc(ngy) Postlarvae

2-3 3-5 5-10 10-15 15-20 20-40

Tm ci (tm c) 50-70

Hng ngy 8-9 9-10 10-11 11-12 12-13 14-15

18-21 (23-30) Tui th ca tm c s thay i theo loi v theo gii tnh, Hothius (1980) cho bit

tui th ca tm s nui th nghim trong ao v cc mu thu ngoi t nhin l 1,5 nm i vi tm c v 2 nm i vi tm ci. Bng 2.5: Mt s c im sinh hc v sinh thi ca tm he

Loi P. monodon P. chinensis P. vannamei P.merguensisTn thng gi Tm s Th Trung Quc Th chn trng Th ui xanhKch c ti a (mm) 360 183 230 Tc tng trng 21-33 g trong 80-

225 ngy25 g trong t hn 5

thng7-23 g trong 2-5

thng 7-13 g trong 76-

112 ngyNhit nui (oC) 24-34 16-28 26-33 25-30Nng mui () 5-25 11-38 hay thp

hn5-35 5-33

Nc/ cht nn Nn y bn Phn b Bin n , Thi

Bnh DngVen bin Trung

Quc, Nam Triu Tin

Ven b TBD v trung tm chu

M

Vnh Ba T, Bin n , ng

Nam Sn lng (%) 61 56 63 Th trng chnh Nht, khp th

giiNht, M M: 70%; Chu

u: 30% Ch thch Tng trng cao v

nhanh nht. Ging t nhin thiu

Thch y bn Nhu cu protein

cao (40-60%); sn lng thp

Tm ln, khe mnh; tng trng

uCh cung cp mt

lng rt nh

Quan trng trong cc m hnh nui

qung canh ng Nam

Ni sn xut chnh Indo, Thai., Mal., Phil., Sri.

Trung Quc, Triu Tin

Ecua., Col., Pana., Peru, M

Indo, Thai, Phil.

Phn phi Min ng chu Phi, ng Nam ,

Nht

Bin Vng, Vnh Bahai, Triu Tin

ng TBD, Mexico-Peru

ng nam

25 i

Bng 2.6: Mt s c im quan trng cn ch khi chn la i tng nui P.

mono don P. chinensis P.

vannameiP. merguensis P. stylirostris P. japonicus

u im

Tc tng trng nhanh, bin mui

rng, n lng cao (65%), v c uy tn trn

th trng

Sinh sn d,thch nn y

bn v bin nhit

thp

Sinh sn d, bin mui

rng, sn lng cao

(65%), tng i khe, t l

sng cao v cho php mt

cao

Ging t nhin, nui

ghp tt, chiu c

ngun nc xu v mt

cao

Ging khng bnh hoc

khng bnh tt, tng trng

nhanh. bin nhit thp hn l loi P.

vannemei

Gi cao Nht trn 40 USD/kg,

d vn chuyn, trng thnh v

sinh sn trong ao v tng trng

nhit thp

Khuyt im

Sinh sn nhn to

kh, ging t nhin

thiu v b dch bnh

nguy him

Nhu cu cht m cao, sn

lng thp, v gii hn nc ngt

thp

Tng trng chm hn

tm s

Tng trng chm v

kch c nh

Vn chuyn kh v c xu hng khng

sng ao

Cn nn y sch, c ct v

cht lng nc tt, mt t v thc n c m

cao

3.10. Tp tnh bt mi v nhu cu dinh dng

a) Tp tnh bt mi ca tm Tm s c xem nh l loi n tp (Dall, 1998), loi n tp c hi (Ruello, 1973), loi n cht vn (Dall, 1968), loi n tht (Hunter v Feller, 1987) hay l loi ch hi ca nhau (Marte, 1980; Leber 1985; Wassenberg v Hill, 1987). Thc n ca tm bao gm gip xc, giun nhiu t, nhuyn th, cc, cn trng, to v cc mnh thc vt. Cc cht vn bao gm cc mnh hu c cng l thc n quan trng ca tm. Tuy nhin, tnh n ca chng cng thay i theo giai on. giai on tm bt v tm ging, chng n nhiu cc loi mnh ng thc vt bao gm lab-lab, vi to, cht vn, thc vt ln, giun, Copepode, Moina, u trng nhuyn th v u trng gip xc. Khi tm ln, chng n cc loi ng vt khng xng sng nh ruc, moi, gip xc chn u, giun nhiu t, nhuyn th; hay c c nh. Giai on ny tm cng n nhiu cc loi cht vn. tm thnh thc, trong sut ma sinh sn, tm n nhiu nhuyn th, trong khi nhng thng khc, tm n nhiu c hn. Hin tng tm n ln nhau xy ra khi tm thiu thc n, thc n thiu cht dinh dng hay mt cn bng trong dinh dng, v nui vi mt qu dy. Tm khe thng tn cng tm yu, tm ln n tm nh v tm v cng n tm v mm. Tm s n sut ngy m, tuy nhin, n nhiu vo ban m. Tm cng n nhiu vo lc triu cao. Tm thch n y v n ven b. Tm gim n vo nhng lc lt xc. Cc yu t mi trng cng nh hng rt ln i vi kh nng bt mi ca tm. Nhit qu cao hay qu thp, oxy qu thp lm tm gim n. Cc yu t khc thay i bt ng thng gy sc cho tm, lm tm gim n.

Tm pht hin v bt mi nh ch yu vo cc c quan xc gic nm u mt ca ru, chn ru, ph b ming v cng. Th gic tm dng nh khng quan trng trong vic pht hin v nh hng mi. Tm dng cng ct thc n thnh mnh nh v a vo ming. Ming v cc ph b ming cng s ct mi thnh mnh nh thch hp trc khi nut. Nhng ht ct hay nhng ht khng n c thng s c thi ra ngay, tuy nhin, c khi chng c n v cc ht ny cn gip nghin thc n. Nhng thc n khng c tiu ha s thi ra cng vi phn.

26 i

Cc enzym tiu ha c tit ra t rut gia s gip tin ha thc n. Cc h vi sinh vt trong rut tm cng c vai tr quan trng trong vic to ra cc enzym tiu ha. b) Nhu cu dinh dng v thc n nui tm Nhu cu cht m v a-xt a-min Cht m l thnh phn quan trng nht trong thc n, c vai tr quan trng trong vic xy dng c th, cung cp nng lng v cc a-xt a-min thit yu. Tm ging c nhu cu cht m khong 40 % (Alava v Lim, 1983). i vi tm tht, thc n c hm lng m thch hp khong 35-40 %. Trong khi , tm b m cn thc n c hm lng m cao khong 45-50 % (Millamera, 1986). C khong 10 a-xt a-min cn thit cho tm c nghin cu bao gm methionine, arginine, threonine, tryptophan, histidine, osoleucine, leucine, lysine, valine v phenylanine. T l cc a-xt a-min trong thc n cng gn vi t l cc a-xt a-min ca c th tm s cho kt qu tng trng tt hn. Nhu cu cht bo

Cht bo c vai tr quan trng i vi tm nh cung cp nhiu nng lng, acid bo cao phn t khng no, phospholipid v vitamin. Hm lng lipid trong thc n cn thit cho tm khong 6-7,5 %. Ngun lipid tt nht cho tm s l t ng vt bin nh du mc, du c, Ngoi ra, thc n c hm lng cholesterol 1% s gip tm ln nhanh, chuyn ha thc n tt, hiu qu hp thu m cao v nng cao t l sng. Ngoi ra, lecithin cng rt cn thit cho tm. Thc n c hm lng 4% Lecithin t u nnh gip tm ln nhanh. c bit lecithin cng rt cn thit i vi nui v tm m. Nhu cu cht bt ng (carbohydrate)

Carbohydrate c vai tr quan trng trong khu phn thc n ca tm khng nhng vic cung cp nng lng, gip hp th cht m m cn c chc nng kt dnh. Hm lng cht bt ng trong khu phn thc n khong 10-20 %. Nhu cu Vitamin v khong

Vitamin v cht khong rt cn thit trong vic iu ha cc tin trnh trong c th. Vitamin B gip vic hp thu protein, carbohydrate v cht bo tt hn; vitamin A v C gip c th c sc khng tt vi bnh tt. Vitamin D cng vi cc cht khong, canxi, phosphorus gip xy dng b v ca tm. Tt c cc Vitamin v cht khong ny d cn vi lng nh nhng rt cn thit b sung c mt cng thc thc n hon chnh. T l Canxi v Phosphor trong thc n nn trong khong 1:1-1,5:1. Lng can-xi trong thc n khng nn vt qu 2 %. Bng 2.7: Nhu cu cc cht a lng trong thc n nui tm

Trng lng tm (g)

Nhu cu m trong thc n (%)

Nhu cu lipid trong thc n (%)

Nhu cu Cholesterol trong thc n (%)

0-0,5 45 7,5 0,40,5-3 40 6,7 0,353-15 38 6,3 0,315-40 36 6,0 0,25

27 i

Bng 2.8: Nhu cu cc Vitamin trong thc n Vitamin Lng/kg thc n Thiamin 50 mg/kg Riboflavin 40 mg/kg Pryidoxine 50 mg/kg Pantothennic acid 75 mg/kg Niacin 200 mg/kg Biotin 1 mg/kg Inositol 300 mg/kg Choline 400 mg/kg Folic acid 10 mg/kg Cyanocobalamine 0,1 mg/kg Ascorbic acid 1.000 mg/kg Vitamin A 10.000 UI/kg Vitamin D 5.000 UI/kg Vitamin E 300 UI/kg Vitamin K 3 mg/kg

Bng 2.9: Nhu cu cht khong trong thc n Cht khong Lng Canxi Ti a 2 % Phosphor 0,8 % Magie 0,2 % Natri 0,6 % Kali 0,9 % St 300 ppm ng 35 ppm Km 110 ppm Mangan 20 ppm Cobalt 10 ppm

3.11. Yu cu mi trng sng

Cc yu t mi trng nc c nh hng rt ln n s phn b, sinh sng, bt mi, tng trng v t l sng ca tm. Theo Boy (1992), cc yu t l, ha, sinh ca nc v t bao gm nhiu yu t, trong , c mt s yu t quan trng nh sau:

pH nc: nc c pH di 4 hay trn 10 c th gy cht tm. Khong thch hp cho tm l 7-9.

mn: kh nng chu ng v thch ngh mn c khc nhau ty loi tm. Thng thng cc loi tm nui c kh nng chu ng mn thp n 5-10 hay thp hn. mn cao 45-60 c th gy cht tm. Hu ht cc loi tm tng trng tt mn 25-30 .

Nhit : nhit tt nht cho tng trng ca tm dao ng trong khong 25-30oC. Mt vi loi c kh nng tng trng nhit di 20oC, nhng nhit trn 35oC c th gy cht tm.

Oxy ha tan: oxy ha tan thp (0,0-1,5 mg/l) c th gy cht tm ty thi gian b tc ng v cc iu kin khc. Hm lng Oxy ha tan tt nht cho tng trng v t l

28 i

sng ca tm nn trong khong gia 3,5 mg/l n bo ha. Oxy ha tan qu bo ha cng gy nguy him cho tm. CO2: hm lng CO2 di 20 mg/l thng thng cha nh hng n tm nu oxy y . H2S: kh H2S rt c i vi tm. Kh ny bt k nng no nu c cng c nh bt li i vi tm. Tuy nhin, nng gy cht tm cha c xc nh. Ammonia: ammonia dng kh NH3 rt c. Hm lng kha trn 1mg/l c th gy cht tm. Hm lng trn 0,1 mg/l cng gy nh hng bt li. pH bng 9 v mn 20 , khong 25 % ammonia dng kh. V th nu hm lng ammonia tng s khong 0,4 mg/l cng s gy bt li cho tm. Nitrite: thng thng, hm lng nitrite trong ao nui khng cao m mc gy cht tm, tuy nhin, nng cao 4-5 mg/l c th nh hng bt li cho tm. II. K Thut sn xut ging tm bin Chn a im xy dng tri ging l khu c bn trong sn xut ging tm, trong , vic la chn a im thch hp l v cng quan trng. Mt s tiu chun quan trng cn lu tm khi chn a im xy dng tri ging nh sau: 1. Nc bin

Nc bin dng cho tri ging nn trong, sch v hn ch ph sa. Cht lng nc n nh, mn dao ng t. Vng ven bin c y ct hay vi nc tt v y quanh nm c xem l rt l tng. Tri xy dng ven b bin y ct hay ny cng hn ch chi ph bm nc v x l nc. Ngc li, nhng ni m ly ca sng vi nhiu ph sa, mn thp v bin ng ln v cht lng nc v chu nh hng ca nc thi, cht c t trong ni a th thng khng thch hp cho tri ging. Cng cn trnh xy dng tri tm ni ng c c dn sinh sng hay gn cc nh my, xng du, ha cht v ngun nc rt d b nhim.

Nc thch hp cho tri ging cn m bo nh sau: - mn: 28-32 - Nhit nc: 28-32 oC - pH: 7,5-8,3 - Oxy ha tan: 5-10 mg/l - Ammonia:

3. Nng lng Trong sn xut ging tm, in l yu cu rt quan trng cho hot ng sn xut v

sinh hot ca tri. Nu tri c xy dng ni c in li quc gia s rt tin li v c hiu qu kinh t cao. 4. Nc ngt

Nc ngt cng l yu t cn xem xt. Nc ngt dng iu chnh mn, ra dng c, v sinh hot khc. Vng c nc ngt t nh my nc cng cng s rt tin li. Nu dng nc ging cng phi xt n cht lng nc.

Nc ngt thch hp s dng trong tri tm cn m bo cc yu t sau: - Nhit : 28-31oC - pH: 7-8,5 - Oxy ha tan: >5 mg/l - cng: >20 mg/l - Fe tng:

hnh hot ng ging dng cho nui ti gia nh

hay i tr

thnh vin hay i tr

ging sn xut bn i tr

Din tch Tn dng din tch t nh quanh nh

2.000-5.000 m2 5000 m2 -1 ha

Sn lng 1-5 triu PL/nm 10-20 triu PL/nm Trn 20 triu PL/nm

S cng nhn, k thut

1 k thut, 2 cng nhn

3 k thut, 3-4 cng nhn

3-6 k thut, 6-10 cng nhn

Tng th tch b 20-100 m3 100-1.000 m3 Trn 1 000 m3

8.2. Trang thit b tri ging a) B lng, b lc, b cha v b x l nc thi B lng, b lc v b cha l nhng b rt quan trng cn phi m bo v tt

trong qu trnh sn xut ging tm bin, nht l nhng vng nc bin khng c trong sch. B lng bng xi-mng ct thp, c th tch ln (trn 100 m3). B dng chm hay bn chm, bn ni. B ny dng cha nc bin cho lng bn, cht rn trc khi bm ln b lc. B c th c che bng mi che ti.

B lc c hai dng l lc xui v lc ngc. B lc xui cho php nc i t trn xung qua cc vt liu lc v vo ngn cha b lc trc khi vo b cha. Nhc im ca dng b ny l lc b nght sau vi ngy s dng. Ngoi ra, n cho nc chy xung qu nhanh v khng tn dng ht b mt ca lc. i vi b lc ngc, nc c bm vo ngn cha y b lc cho nc dng ngc ln mt v i vo b cha. u im ca b ny l nc chy qua lc chm v ton b mt lc c tn dng. Lc c th c sc ra d dng bng cch bm nc t mt xung y. Ngoi ra, cn c dng lc ngang. Dng lc ny cng c u im nh lc ngc. c cc dng lc, vt liu lm lc bao gm cc loi nh ct, nh, than hot tnh v san h.

B cha dng cp nc trc tip cho cc b ng nui. B cha phi m bo t nht 20% th tch b ng sn sng cp thay nc khi cn thit.

B x l nc thi l mt trong nhng yu cu quan trng trong mt tri ging nhm hn ch nc thi lan trn, lm nhim mi trng xung quanh. B cha xy chm, bng ximng. B c th tch ln 20-100m3 cha nc thi v x l trc khi cho ra mi trng ngoi.

31 i

Hnh 2.9 : Tri tm ging s 1 (Bc Liu) (tri) v h thng lc nc bin ca trt (phi) (Ngun: Phng 2003)

b) B nui v tm b m Trong sn xut ging, tr ngi ln nht l thiu ngun tm b m t nhin. V th,

vic nui v tm b m l khu rt cn thit ch ng sn xut. B nui v tm b m c th l b xi mng, composite hay b lt tm nha. B c th c dng trn, ch nht hay oval. y b phng hay hnh chp. Ty theo qui m v mc nh khc nhau, th tch b c th t 5-40 m3 v su 1m. B qu nh s nh hng n qu trnh rt ui ca tm khi bt cp. B c mu en l tt nht cho nui v v trng ca tm. Khi nui vi thi gian di (trn 5 tun), y b cn tri mt lp ct. B lp t ph hp vi vic nc chy trn lin tc. c) B cho

Trong mt tri hon chnh lun c b cho tm ring bit vi b nui v hay ng u trng. B c th bng nha hay composite. Th tch b 50 lt n 1,5m3. B nn c dng trn y phng hay chp. B dng cha tm sp n khi tm . d) B ng u trng

C hai h thng b khc nhau dng cho ng nui u trng tm bin. H thng b ln c p dng ch yu Nht Bn v i Loan v h thng b nh cn gi l h thng Galveston hay h thng b ng Nam .

H thng b nh B c dng trn, ch nht, vung hay oval vi th tch 4-6 m3. B lm bng

ximng, nha cao cp hay composite. B c y phng hay chp. B c lp t cc ng PVC cp v thay nc

H thng b ln B thng c dng cha nht hay vung vi th tch 50-2.000 m3 (5 x 5 x 2 m hay

20 x 50 x 2 m). B c th t nogi tri hay trong nh vi mi che nha trong sut. y l b dng chung cho c vic cho , n, ng u trng v postlarvae n PL25-30.

H thng tun hon H thng b tun hon bao gm cc b ng v b lc sinh hc. B ng tt nht

bng composite, mu xm, trn, c th tch 4-10m3. B c ni vi b lc sinh hc nh h thng ng PVC.

B lc sinh hc c th l b lc ngp nc hay c kt hp vi lc t. Mi loi c u im v nhc im ring. Tng th tch b lc khong 20-30% tng th tch b ng. B c th bng compotise hay bng nha, c th tch 0,5-1 m3/b. Cc b c lp rp vi cc ng nha PVC sao cho nc c lu thng tt gia cc b lc v vi b ng u trng. Gi th cho b lc c th bng nh, san h hay ht nha sao cho nh v c tng din tch b mt ln. i vi b lc ngp nc, cn phi sc kh cho b m bo Oxy cho b Vi khun pht trin tt. Nn b tr nhiu cm b ng v b lc gim ri ro v d x l khi c bnh tt.

e) B ng Postlarvae Trong tri tm ging, h thng b ng Postlarvae hay ao ng l rt cn thit. Cc

b ng c th xy bng ximng, th tch 5-10m3. B c th t ngoi tri. Tri vi qui

32 i

m ln thng c ao ng. Din tch ao t 500-1000m2. Ao thit k c dc, c h thng cp tho nc hon chnh. su b v ao m bo mc nc 60-80cm.

f) B nui to v b p trng Artemia Nui to v Artemia hay cc loi thc n t nhin khc l khu quan trng trong tri

tm ging. Tri ln cn c mt phng th nghim v khu nui to, lun trng ngoi tri. Nui to v lun trng c th t nhng dng c nh trong phng th nghim nh ng nghim, bnh tam gic, keo ln n nhng b 20 lt - 20 m3 t ngoi tri. Cc b ln c th lm bng composite, nha hay ximng. Th tch b nui thc n t nhin chim khong 20 % tng th tch b ng u trng.

g) H thng sc kh Sc kh l khu lun c duy tr xuyn sut trong qu trnh ng nui ca tri

ging nhm m bo Oxy ha tan trong nc, m bo nhit u trong b, gim hm lng kh c, phn tn u trng v thc n. Sc kh c th bng my thi hay my nn, chy bng nhin liu hay in. Tuy nhin, my chy bng in th tt hn hm trnh nh hng ca du ln u trng. Nn c t nht 2 my dng lun phin nhau m bo an ton cho my v m bo sc kh c lin tc. Hai my ny nn c lp t pht v tt t ng.

My thi c p sut hi 0,2-0,3 kg/cm3 v tc thi 4-5 lt/m2/pht s m bo oxy ha tan cho tm.

h) H thng cp, thi nc H thng bm v ng nc trong tri tm cn c lp t hon chnh m bo

vic cp thi nc d dng cho cc b. Ty theo c im thy triu v cht lng nc bin m c th dng nc mt hay nc bin t b lc ngm di nn y ct. Tuy nhin, nu bm nc bin ngm s m bo ch ng hn v cht lng nc cng tt hn mc d vic xy dng b lc ngm cng khng n gin. Ty theo cng sut v qui m tri m c th dng bm vi cng sut thch hp. My bm in s tin li rt nhiu so vi bm du. Nc bin bm vo s qua b lng, b lc, b cha v dn xung cc b ng nui bng dn lc. Nc thi trc khi x ra ngoi mi trng cn cho qua b x l v dng ha cht x l k lng, trnh ly lan.

Nc s dng ng u trng cn c x l k bng bt ty vi nng 2,5 mg/l. Nc Javel (nng 5,25 % NaOCl) cng c th s dng vi liu 3,5 ml/100 lt nc. Sau khi dng chlorine, c th trung ho bng thiosulphate natri vi nng ging nh Chlorine. Sc kh mnh khong 15-24 gi trc khi s dng. Tuy nhin, nu nng Chlorine s dng thp th khng cn trung ho bng Thiosulphate Natri v c th gy c cho u trng. Sau , dng EDTA vi lng 10 mg/l x l tip. i vi nc thi, cn x l vi liu cao hn 100-200 mg/l.

i) Cc dng c khc Ngoi cc b, cc h thng in, nc; trong tri tm ging cn yu cu rt nhiu

my mc v cc dng c khc s dng trong qu trnh sn xut. 9. Nui v tm b m

9.1. Ngun tm b m Hin ti, tm b m dng cho sinh sn nhn to c th t hai ngun: tm t nhin

bt t bin v tm nui trong cc ao, m. Ty theo ngun tm khc nhau m c th c nhng u khuyt im khc nhau v ty tng ni m dng ph bin tm bin hay tm

33 i

m. Nhn chung, tm m c kch c nh hn tm bin, cho sc sinh sn thp v cht lng u trng i khi cng thp hn. Tuy nhin, tm m gip ch ng ngun tm b m nht l nhng vng v nhng ma t tm bin phn b; gi thnh tm m cng r hn tm bin gp nhiu ln. c nhiu th nghim gia ha ngun tm b m qua nhiu th h nui trong iu kin nhn to v cho thy c rt nhiu u im. Nhn chung, tm bin c kch c 150-300g, tm m 100-150g c th c chn lm tm b m nui v.

9.2. Th nui Tm b m sau khi chuyn v n tri phi c chn k v c thi gian thch nghi.

Nhng con tm cha thnh thc hay chm thnh thc, khe mnh, v sch s v cng, khng thng tch, mang bnh thng (khng c mu , vng hay en) c chn nui v. Sau , tin hnh x l tm b m bng formaline 200 mg/l trong 30 pht. Mt tm b m 6 con/m2 (3 c:3 ci).

Hnh 2.10: Tm s b m (tri) v h thng b tun hon dng nui v tm m

9.3. Ct mt a) C s khoa hc ca vic ct mt tm Trn thc t, tm b m bt t bin v nhiu trng hp c th cho c ngay

trong m hay hm sau m khng cn phi ct mt nui v. l do tm thnh thc chn mi (giai on IV). Tuy nhin, a s cc trng hp tm cha thnh thc, tm m cn c ct mt trc khi nui v sm thnh thc v trng.

Thng thng, qu trnh thnh thc ca tm b c ch bi hormon c ch sinh dc (GIH). Hormon ny c tit ra t mt c quan X trong cu mt. Hormon c chuyn n cha tuyn nt tit vo mu. Khi ct mt tm m s lm lng hormon ny gim n mc thp qu trnh thnh thc ca tm c th din ra nhanh chng. Tuy nhin, khng nn ct c hai mt tm v s lm nh hng n s thng bng, iu ha p sut thm thu, bin i sc t v lt xc ca tm vn lin quan rt ln n mt.

b) Cc bc chun b ct mt tm - Ch chn tm ci ct mt v loi b tm b thng tch, khi ct mt gi tm

nh nhng v chc chn bng mt tay. - Kim tra thelycum ca tm ci, ch nhng tm c cha ti tinh mi c ct

mt. Tm ci cha c ti tinh nn gi li n khi no chng lt v v giao v xong mi ct mt.

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- Ch ct mt mt tm (mt phi hoc mt tri). Gi li mt khe, ct mt h khi nu c.

- C th ct mt tm bng mt trong cc phng php sau: - Rch v bp cu mt - Tht cung mt - t cu mt bng in hay bng thanh Nitrate bc - Ct cung mt bng ko

c) Mt s nh hng ca vic ct mt tm nui v Khi tm c ct mt, qu trnh pht dc, sinh sn, s lng v cht lng trng

cng nh s lng v cht lng u trng c th c nh hng nht nh. - S lng trng trn mi ln t hn so vi tm t nhin - Tng s trng qua cc ln tm nhiu hn tm m thnh thc t nhin do

nhiu ln - Tm ct mt v khng ct mt u gim st s lng trng qua mi ln . - Nui v qua nhiu th h c th lm gim sc sinh sn ca tm, nhng nu c

chn lc tt c th lm tng s lng trng - Tm ct mt lt xc sm hn tm khng ct mt - Tm ct mt c t l sng thng thp hn tm khng ct mt - T l n ca trng ca tm ct mt thng thp hn khng ct mt. Tm nui

trong ao/m ct mt c t l n trng thp hn tm t nhin ct mt - T l n ca trng gim dn qua cc ln - Mu sc trng tm ct mt c khc so vi mu sc ca trng tm t nhin - T l sng ca u trng t tm nui v thng thp hn so vi t l sng u

trng t tm t nhin 9.4. Qun l mi trng nui tm b m

Trong nui v tm b m, qun l mi trng b nui l khu rt quan trng. Cht lng nc bao gm cc yu t nh mn, nhit , pH, nh sng, Oxy ha tan, m, kim loi nng, cht hu c, l nhng yu t cn c gi thch hp. mn: 28-35ppt

- Nhit nc: 25-30 oC - pH: 7,5-8,5 - Chu k chiu sng: T nhin - Cng nh sng: 100 lux hay di - Oxy ho tan: >5 mg/l - m tng s:

9.5. Thc n v cch cho n Cc loi thc n thng dng cho tm b m tri ging l mc, s huyt, hu,

hu, c mn hn, gan heo vi lng 10 % trng lng tm. Cc loi giun nhiu t (con ri) c vi nhiu HUFA cng c xem l thc n tt cho tm, nhng cha c ph bin. Ngoi ra, thc n cng nghip cng ang c pht trin nhm m bo nhu cu v cht cho tm b m, s trng v cht lng u trng. Trong thnh phn ca thc n cng nghip, ngoi cc yu t Protein th (35-40 %) v lipid th (6 %), cc yu cu v a-xt amin, ngun m, loi a-xt bo c bit HUFA, cc vitamine, khong cng rt c ch . Thnh phn cc a-xt bo quan trng nh 18:2n6 nn chim 0,4 %, 18:3n3 chim 0,3 %, 20:5n3 chim 0,4 %, 22:6n3 chm 0,4 %. Thnh phn cholesterol chim 0,25 %. Thnh phn mt s Vitamin quan trng nh trnh by bng. Trong qu trnh nui v, tm c cho n 2 ln/ngy. Thc n tha nn c siphon sch s. Bng 2.11: Thnh phn mt s Vitamin quan trng trong thc n ca tm Vitamin Lng Thiamin Riboflavin Asscorbic acid Vitamin A Vitamin D Vitamin E Viamin K

50 mg/kg 40 mg/kg

1.000 mg/kg 10.000 UI/kg

5.000 UI/kg 300 mg/kg

5 mg/kg 9.6. Cho v cho n trng

Thi gian nui v tm c th t 3 ngy n 2 thng ty vo tui, kich c, giai on lt xc, thc n,... Tm (nui v hay t t nhin) chn cho cn t mt s tiu chun nh (i) bung trng giai on IV (mu xanh m i vi P. monodon; mu xm en i vi P. merguiensis v P. indicus); (ii) cc ph b y , khng thng tch; (iii) c ti tinh ti cha tinh; v (iv) tm c mu bnh thng

Trc khi cho , tm cn c x l bng ha cht nh Formaline, KMnO4,.. Sau khi cho tm vo b chun b k, cn che ti li vi vi bt v trnh lm ng tm. Tm s ngay trong m . C th nhn bit tm bng mi c bit v qua nhng vn bt trn mt nc. Sng hm sau, vt tm m ra khi b v siphone trng vo ti lc mn. Trng thu c nn x l bng formol, Iodine hay KMnO4 trc khi em p. Mt trng p c th t 100-200 trng/lt. Trng c th p trong nhng b p ring bit sau chuyn u trng vo b ng hay p trc tip trong b ng u trng. Trng s n 12-15 gi sau khi p. 10. ng nui u trng

10.1. ng nui u trng trong h thng b nh (m hnh Galveston) a) Th ng Nauplius sau khi chuyn n b ng, nu nhit v mn gia nc vn

chuyn v nc b ng chnh lch khng qu 0,5oC v 1 th khng cn phi thun ho, nhng nu c s chnh lch ln th phi thun ho trc khi th. Mt ng ca u trng trung bnh 150-200 Nauplius/lt nc.

b) Mi trng nc ng Nhit , mn, Oxy ha tan, nh sng, thay nc, x l ha cht l nhng yu t

quan trng cn c kim sot qun l mi trng ng. Nhit nc nn duy tr

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khong 28-30oC. Nhng thng lnh, cn s dng dng c tng nhit l rt cn thit, ng thi y b li cng l bin php hu hiu. mn nc ng tt nht l 28-30 . i vi tm th (P. merguiensis v P. indicus), mn thp n 22 cng c th s dng c. Tuy nhin, nc bin thng c mn dao ng rt ln theo ma, v th vic cha nc mn d tr l rt cn thit m bo sn xut quanh nm. Ngoi ra, nc t (90-120) cng c th dng pha nc ng thay th nc bin khi cn thit. C th che ph b vi tm bt gi ti b, n nh nhit , to khng pht trin qu mc v trnh ly lan bnh. Tuy nhin, nh sng n neon 4 bng/b cng khng nh hng n tm. nh sng ny cn thit cho lm vic trong tri. Sc kh lin tc m bo hm lng Oxy m 5 mg/l. Hm lng N-NO2- v NH3 m bo di mc gy hi. cc tri sn xut ln cn trang b thm dng c kim tra nhanh nng m pht hin v x l kp thi.

Trong qu trnh ng nui, khng cn phi thay nc trong giai on nauplius. Giai on Zoea thay nc 30% mi ngy v giai on Mysis thay nc 50% mi ngy, giai on post-larvae thay 50-80% mi ngy. Ngoi ra, cng c nhiu thnh cng trong vic ng nui u trng vi ch thay nc rt hn ch hay ngay c khng thay nc trong sut thi gian ng, tuy nhin, ch cho n phi tht cn thn. Cn phi ht cn y b hng ngy trc khi thay nc.

c) Thc n v cch cho n Giai on nauplius, u trng dinh dng bng non hong v th khng cn cho n.

Tuy nhin, vic cho n nn bt u t giai on nauplius 4 cung cp thc n kp thi cho u trng khi chng chuyn sang giai on Zoae1.

Thc n cho u trng Zoae bao gm cc loi vi to nh Skeletonema costatum, Chaetoceros sp, Tetraselmis, Isochrisis,... Tuy nhin, Skeletonema costatum v Chaetoceros sp. c xem l a thch v tt nht cho u trng Zoae do c chui di v hm lng cht dinh dng cao. Mt cho n i vi to ny 60.000-120.000 tb/ml. To Tetraselmis v Isochrysis cho n vi mt 10.000-30.000 tb/ml. y l cc loi to ti, nhng tt nht l to mi thu v ang giai on pht trin hay u giai on qun bnh ca chu k pht trin ca to nui. To cn c lc qua ti lc, loi b nc to.

Ngoi to ti, to kh (Spirulina sp.) cng l thc n b sung quan trng hay ngay c thay th cho to ti. To kh rt giu m v cc cht cn thit khc. Lng cho n trung bnh 1-2 mg/m3/ln.

Thc n nhn to (microencapsultated hay artificial plankton) hin ang c s dng rt ph bin cc tri tm ging, rt tin li v thnh cng. Thc n nhn to c th b dng sung, thay th mt phn hay ngay c s dng cng vi to kh thay th hon ton to ti. Lng cho n trung bnh 0,5-1 g/m3/ln. u trng cho n cch 3 gi/ln.

i vi u trng Mysis, ngoi cc loi to trn vi s lng c gim dn (to 50.000-75.000tb/ml i vi Skeletonema costatum v Chaetoceros; 20.000-30.000 tb/ml i vi Tetraselmis), u trng cn cho n vi u trng Artemia mi n. Mt Artemia cho n thay i t 0,25-1,0 con/ml nu c b sung thc n ch bin, hay 0,5-8 con/ml nu khng c b sung thc n ch bin. Artemia c cho n t giai on Zoae3 c thc n sn sn khi u trng chuyn sang Mysis. Ngoi ra, cn c th cho u trng Mysis n thm Rotifer (Brachionus plicatilis) vi mt 20 con/ml. Rotifer s rt quan trng cho u trng nu nh c lm giu ho vi a-xt bo cao khng no (HUFA). Thc n nhn to cho n vi lng 1-2 g/m3/ln. Tuy nhin, ngi ta thnh cng trong vic ng u

37 i

trng hon ton bng thc n nhn to v to kh m khng cn to ti hay u trng Artemia.

T giai on PL1 n PL15, tm c th c chuyn sang b khc hay vn ng b c. Lng to cho n gim xung hay ngng hn. u trng Artemia dng vi mt 1-2 con/ml nu c b sung thc n nhn to hay 6-20 con/ml nu khng c thc n b sung. Lng thc n ch nhn to khong 1-2 g/m3/ln v thc n ch bin (trng g v tm xay hp cch thy) 5 g/m3/ln. T giai on PL15 tr i, c th chuyn tm sang ng trn b ximng, ao t hay giai li.

10.2. ng nui u trng theo h thng tun hon H thng tun hon t lu c nghin cu ng dng. Hin nhiu ni trn th

gii cng p dng m hnh ny trong sn xut ging. BSCL, ng nui u trng theo h thng tun hon hin ang ph bin cc vng ni a.

V nguyn tc, cch chm sc cho u trng n cng tng t nh i vi m hnh Galveston. Tuy nhin, mt nui thng thp hn, khong 100-150 u trng/l. Trong giai on t nauplius n mysis, khng thay nc hay lu thng nc vi b lc sinh hc. Vic lu thng nc b ng vi b lc sinh hc c th thc hin t giai on Mysis2, Mysis3 hay postlarvae 1 ngy tui ty mi trng nc b ng.

B lc sinh hc c chun b trong thi gian chun b b ng nui. C th dng vi sinh (Bacilus hay Nitrosomonas) gy vi khun cho b lc v b sung NH4Cl vo b (0,5-1 mg/l) kch thch vi khun pht trin. Sau khi vi khun pht trin tt v hm lng NH4Cl gim xung cn di 0,1 mg/l (khong 10 ngy sau khi t vn hnh), th nn cho nc b ng lu thng vi nc b lc sinh hc. Lc , u trng giai on Mysis2 tr i.

ng nui u trng theo m hnh tun hon c u im l t tn km nc, mi trng nc n nh, t bin i ln. Do hn ch dng thuc khng sinh trong qu trnh ng nn u trng khe. Tuy nhin, khi gp tr ngi v bnh tt s kh x l hn m hnh Galveston.

Hnh 2.11: H thng ng u trng h/thay nc (tri) v kn/lc tun hon (phi)

10.3. ng nui u trng trong h thng b ln

y l phng php ng u trng kh ph bin ph Nht bn v i Loan. B ng ln 40-200m3 c xy ngoi tri, khng c mi che. Mt u trng 20-60 nauplius/lt. Sau khi th u trng, cy to khu vo b v bn phn gy mu v to thc n t nhin cho u trng. Phn bn cho b gm KNO3 (3 mg/l) v Na2HPO4 (0,3

38 i

mg/l). Trong qu trnh ng, nc mi c cp vo t t m rt hn ch thay nc. Ty theo s pht trin ca to m thm nc vo gim mt hay bn phn tng mt to.

Giai on mysis cho n Artemia mi n v c thc n cng nghip nhng vi liu lng rt thp. Giai on postlarvae, thc n ch bin c b sung ngoi Artemia.

Phng php ny tn dng c thc n t nhin nh to, rotifer,... pht trin t nhin nh bn phn, v th gim c lng cho n. Vi qui m sn xut ln, cng vic n gin, chi ph thp, phng php ny rt ha hn Tuy nhin, kim sot mi trng ng i khi gp nhiu tr ngi v tm P. japonicus thch hp vi phng php ny hn P. monodon. 11. Vn chuyn v thun ha tm

Vn chuyn v thun ha tm l mt trong nhng khu rt quan trng trong qu trnh sn xut ging. Vn chuyn v thun ha tm b m, u trng Nauplius, v postlarva i hi nhng yu cu k thut khc nhau.

11.1. Vn chuyn v thun ha tm b m Tm b m c th c thu gom t ngoi bin hay t cc ao m nui. V th, thi

gian vn chuyn c th ch rt ngn (di 30 pht) n rt di (trn 3 ngy). Dng c chuyn tm b m tt nht l thng xp, kch c 0,3 x 0,4 x 0,5 m. Thng cha 1/3 nc v c sc kh lin tc bng my thi kh nh (air-pump). Mt vn chuyn l 5-7 con/thng. Thng c np y v c l thng kh. Ty theo trng hp m c th vn chuyn bng tu hay ghe. Trong thi gian vn chuyn nht l vn chuyn ng di, nn gi nhit thp bng cch chum nc xung quanh hay tt nht nn chuyn bng xe my lnh. T l sng thng t cao trn 90 %. Tuy nhin, i khi cng gp nhng tr ngi lm hao ht ln nht l khi tm b m yu. Bnh thn tm b m sau khi vn chuyn l mt trong nhng tr nga.

Sau khi chuyn n tri, cn th tm b m nui dng 5-7 ngy trc khi ct mt nui v. m bo mn nc b nui ging mn nc vn chuyn.

11.2. Vn chuyn v thun ha u trng Trong thc t, khi ngun tm b m ti a phng khan him, vic mua v vn

chuyn tm b m v u trng t ni xa v ng l rt cn thit. Tuy nhin, vn chuyn u trng mi n (Nauplius) i khi thun li hn tm b m. u trng nauplius c vn chuyn bng bao nha cha 8-10 lt nc vi mt 50.000-80.000 u trng/l. Phng vn chuyn c th bng my bay, xe hay tu nhng m bo thi gian vn chuyn khng qu 15 gi. T l sng u trng thng t cao trn 95%. Trc khi th ng, cn phi thun ho nhit v mn cho u trng bng cch ngm bao vo nc ng 15 pht v sau cho nc ng vo bao t t. Tuy nhin, nn m bo nc ng v nc vn chuyn khng chnh lch ln v mn.

11.3 Vn chuyn v thun ha tm Postlarvae Cng ging nh vn chuyn v thun ha u trng, vn chuyn tm postlarvae bng

bao nha. Tuy nhin, bao c kch c nh, cha 2-3 lt nc/bao trnh hao ht ln cho tm trong qu trnh vn chuyn. Mt tm l 500-2.000 con/l ty kch c PL v thi gian vn chuyn. Phng tin chuyn tm cng c th bng my bay, xe hay tu. Thi gian vn chuyn di 7-12 gi, nn khng ch nhit lnh cho tm. Cch thun ha tm post-larvae cng nh u trng. Thi gian thn tha tm nh sau: Bng 2.12. Thi gian thun ho nhit v mn tm postlarvae (Maugle, 1987)

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Chnh lch nhit (oC) Chnh lch mn () Thi gian thun ha (pht) 0 2 4 6 10 12 14

0 1 2 3 5 6 7

4-6 20 40 60 100 120 140

12. nh gi cht lng tm sinh sn Trong qu trnh sn xut ging bao gm nui v tm b m v ng u trng, c rt

nhiu yu t c th nh hng n cht lng trng v u trng. Mt s thng s quan trng lm c s cho vic nh gi cht lng sinh sn ca tm nh sau:

- Sc sinh sn thng qua s lng trng trn mt ln ca tm. - Kch c trng - Sinh ha ca trng - Thi gian pht trin phi - T l n ca trng - Tnh hng quang ca nauplius - Sinh ha ca u trng - T l sng ca cc giai on u trng - Kch c cc giai on u trng - Thi gian ng u trng - Hnh dng, kch c v trng lng ca postlarvae - Kh nng chu sc ca postlarvae - Thnh phn sinh ha ca hu u trng - T l rng rut so vi c - Tng trng v t l sng ca tm trng thnh.

13. ng tm postlarvae ln ging 13.1. Ao ng

Ao ng nn c hnh ch nht di bng 4-5 ln rng v din tch dao ng t 250-1.000 m2 ph hp vi kh nng chm sc qun l qui m nh. Ao phi gi c mc nc n nh trong thi gian ng. Mc nc t 0,6-0,8 m l va phi v mt b phi cao hn mc nc ti a l 0,4 m. y ao nghing v pha cng thot 1,5 % gip thu tm d dng. Ao nn c 2 cng (cp v thot) nm v 2 pha vic qun l nc c thun tin

13.2. Chun b ao ng Sn vt sch lp mn b hu c y, ba y ao cho bng phng v phi y ao

cho do. Dng vi x l ao vi lng 8-12 kg/100 m2 i vi ao c hay 15-20 kg/100 m2 i vi ao mi o. C th dng bt ht tr (cha saponine) hay dy thuc c (cha rotenon) loi ch hi trc khi th ging.

Bn phn gy mu nc bng phn hu c (25-30 kg/1.000 m2) hay phn v c (NPK hay DAP vi lng 2,5-3 kg/1000 m3). a nc vo ao khong 0,3-0,4 cm qua li lc mn 0,5-0,7 mm hay di 1mm dng 2 lp trnh ch hi vo ao. Gi mc nc ny 2-3 ngy cho thc n t nhin pht trin, sau , cho nc vo n mc 0,6-0,8 m trc khi th tm ng.

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13.3. Mt th, t l sng v tng trng ca tm Tc tng trng ca tm ph thuc nhiu vo mt . Mt ng thch hp

dao ng t 50-200 PL/m2. Thng thng tng trng ca tm con ng t Postlarvae ln ging khng sai khc ln trong tun u d mt c khc nhau. T tun th 2 tr i ln ca tm bt u thy khc bit. Nu tm th mt cao (125 con/m2) tc tng trng c th gim sau tun ng th 5. T l sng c th t n 70 % sau 25-30 ngy ng.

13.4. Cho n, chm sc Thc n cho tm bao gm cc loi c hp (1-2 kg/10.000 con/ngy), thc n ch bin (0,5 kg tht tp v 5 trng g cho 10.000 tm/ngy) hay thc n cng nghip (0,5kg /10.000 tm/ngy). Cho n 4-5 ln/ngy v cch nhau 5-6 gi. Thay nc 30 % hng ngy i vi b hay hn ch thay nc i vi ao nhng phi duy tr c mu nc tt.

13.5. Thu hoch tm Thi gian ng tt nht l 2 tun. Thu tm c th bng nhiu cch khc nhau nh dng vt bt bt ri tho cn hay tho nc qua cng tm vo ti li hay giai ngoi cng. Ni chung phi ht sc cn thn sau khi thu tm trnh tm b xy xt, tm yu s hao ht nhiu khi th vo ao nui tht.

Hnh 2.12 : Ao ng tm s bt ln ging (tri) v h thng ng tm (phi)

III. K Thut Nui Tm Thng Phm 1. c tnh k thut ca cc m hnh nui tm bin C rt nhiu m hnh nui tm bin ang c p dng trn th gii v Vit Nam, mi m hnh nui ngoi cc c tnh k thut cung th cn c tnh c th theo vng sinh thi. Trc y, hnh thc nui tm bin c phn chia thnh qung canh, bn thm canh, thm canh v siu thm canh. Song hin nay c xu hng phn chia thnh hnh thc nui nng sut cao (hn 3 tn/ha/v) v nng sut thp (1-3 tn/ha/v) (Chanratchakool v ctv 1997). Nhiu hnh thc nui mi cng c xut nh nui sinh thi (organic farming). Tuy nhin, vic phn chia cc hnh thc nui cng c tnh tng i, v ty vo tng quc gia. Vit Nam, mt s hnh thc nui cng c nh ngha trong tiu chun ngnh thu sn.

1.1. Nui qung canh (Extensive culture) L cc hnh thc nui da hon ton vo thc n t nhin trong ao. Mt tm

trong ao thng thp do l thuc vo ngun ging t nhin. Din tch ao nui thng ln (cn gi l m nui) t sn lng cao. u im ca hnh thc ny l vn vn hnh thp v khng tn chi ph ging v thc n, kch c tm thu hoch ln, gi bn cao, cn t

41 i

lao ng cho mt n v sn xut (ha) v thi gian nui thng khng di do ging ln. Nhc im l nng sut v li nhun thp, cn din tch ao nui ln tng sn lng nn vn hnh v qun l kh, nht l cc ao m t nhin c hnh dng rt khc nhau. Hin nay m hnh ny ang b hn ch do gi t tng.

1.2. Qung canh ci tin (Improved extensive culture) L hnh thc nui da trn nn tng ca m hnh nui tm qung canh nhng c th

thm ging mt thp (0.5-2 con/m2) hoc b sung thc n khng thng xuyn, i khi b sung c ging v thc n. Hnh thc nui ny thng l thu t th b. nc ta cc m hnh nui kt hp trong rng ngp mn, nui trn t nhim mn theo ma, thuc hnh thc ny. u im ca m hnh l chi ph vn hnh thp, c th b sung ging t nhin t thu gom hay ging nhn to, kch c tm thu hoch ln, gi bn cao, ci thin nng sut ca m nui. Nhc im l phi b sung ging ln trnh hao ht do ch hi trong ao nhiu, hnh dng v kch c ao, m theo dng qung canh nn qun l kh khn. Nng sut v li nhun vn cn thp.