Xây Dựng Mô Hình Nuôi Không Thải Nước

B Nng nghip v Pht trin Nng thn

BO CO TIN

D N NUI THM CANH C BIN TRONG AO BNG MNG NI (CARD VIE 062/04)

MS5: Xy dng m hnh nui khng thi nc

Tc gi: Michael Burke, Hong Tng & Daniel Willet

12/2007

Bo co K thut s 5, D n Nui thm canh c bin trong ao bng mng ni CARD VIE 062/04

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Xy dng m hnh nui c bng mng ni khng thi nc thi ra mi trng

D.J. Willett1, C. Morrison1, M.J. Burke1, L. Dutney1 & T. Hoang2

1Department of Primary Industries and Fisheries, Bribie Island Aquaculture Research Centre, Bribie

Island, Queensland, Australia. 2Nha Trang University, International Centre for Research and Training, NHATRANG City , Vietnam

Correspondence: Daniel Willett, Bribie Island Aquaculture Research Centre, PO Box 2066 Bribie Island, Queensland, 4507 Australia. [email protected] Ngi dch: Hong Tng v Lu Tng Ngc Hiu (HNAQUA) ___________________________________________________________

Tm tt Trong cc ao nui trng thy sn thm canh, vn qun l cht lng nc v qun l cht thi thng gp nhiu kh khn do lng cht thi kh ln tch t trong qu trnh nui. Kt qu thu c t cc d n CARD cho thy sc sn xut ca h thng mng ni t trong ao nui nc chy kh cao, c th t nng sut hn 35 tn/ ha (nng sut chung ca mulloway v whiting). Hin ti vic thay nc hng ngy vn l bin php ch yu c p dng (vi mc thay nc hng ngy trung bnh l 10% - xem MS No.4) qun l cht lng nc trong h thng nui nc chy. Tuy nhin bin php ny hin nhin khng c khuyn khch do th hin tnh bt hp l trong vic s dng ngun li nc v gy ra nhiu tc ng mi trng do nhim cht thi. Mt trong nhng mc tiu hng u ca d n l tm hiu cc gii php hn ch nc thi n mc ti thiu m vn m bo em li nng sut bn vng cho h thng nui nc chy. Bo co sau y nhm tm tt chi tit kt qu th nghim thu c t cc gii php hn ch thay nc, trong qu trnh tin n pht minh mt h thng nui thy sn hon ton khng nc thi. Trong gii php u tin, mt h thu cht thi c a vo h thng nui nc chy thu cht thi v thc n tha, ng thi gim ngun nhim hu c vo ao nui. Mt nghim thc i chng khng s dng h thu (nc thi c x trc tip ra ngoi mi trng) c thc hin ng thi xc nh hiu qu thu cht thi rn ca h thng thng qua so snh cc ch tiu Tng cht rn (TS), Tng Nit (TN) v Tng Phosphat (TP) ca hai nghim thc. Kt qu nghin cu cho thy vic t h thu thi trong ao nui nc chy nhm lng cht thi rn loi b nh k l khng my hiu qu. iu ny c th c l gii do ng thi dng chy trong ao nui kh cao nn gy ra xoy nc v khuy ng cc cht thi rn khin chng khng th lng xung khu vc h thu c. Thm vo , c nui trong ao cng lin tc khuy ng v lm cc cht thi lng ng b sc ln ln na. Tuy nhin, xt v mt x l cht thi th h thng h thu ny vn c kh nng hot ng hiu qu nu c s dng trong mt ao x l tch bit ring vi ao nui. Mt mc tiu khc ca d n l tm hiu tc ng ca rong Asparagopsis armata nh mt tc nhn hp th cht thi. Cc nghin cu trc y ca nhiu tc gi BIARC cng xut kh nng pht trin rong bin nh mt tc nhn lc sinh hc trong cc ao nui thy sn, mt s nghin cu mi nht v vic s dng to A. armata trong lnh vc ny cho thy Asparagopsis armata th hin nhiu u th hn


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hn so vi cc loi to lc thng dng hin nay. Cc kt qu nghin cu trn m ra mt hng i mi trong vic s dng Asparagopsis armata trong nui trng thy sn. Tuy nhin, tr ngi ln nht trong vic s dng loi to ny l nhng kh khn trong vic thu ging v nui sinh khi vi qui m ln, c bit l vic thu to giai on bo t 4 thng gp tht bi (do to khng sinh trng hoc thm ch tn trc pha thu hoch). Cc nguyn nhn c lin quan ang tip tc c nghin cu. Hin ti, BIARC ang nghin cu pht trin nhiu bin php khc phc cc tr ngi nu trn vi nhiu kt qu kh quan, bo hiu kh nng ng dng A. armata lm tc nhn lc sinh hc trong tng lai khng xa. Hin nay, rt nhiu nghin cu khoa hc trn th gii chng minh s thnh cng ca qu trnh lc sinh hc nh vi khun (thut ng x l Bio-floc) trong vic qun l cht lng nc ca cc ao nui thy sn. Cng ngh ny ch yu da trn vic duy tr mt t l (Carbon:Nitrogen) lm c s thc y qu trnh phn hy d dng. Mt lot th nghim c tin hnh nghin cu hiu qu ca cng ngh bio-floc khi s dng kt hp vi h thng nui nc chy, c th l c s dng nh mt b phn x l ri pha ngoi ca h thng tun hon nc. Kt qu th nghim xc nh c t l Carbon ti u cn p dng trong cng ngh bio-floc hn ch ti a cc hp cht Nit c hi cho thy sinh vt (TAN v NOx) thng c trong nc thi ca h thng nui.Thi gian x l khong 12 gi v tnh hiu qu cng c duy tr ko di trong mt khong thi gian lu hn thng thng trc khi h thng x l cn c ti khong ha. Vic chuyn i mi trng nc thi t ch b to chim u th sang vi khun chim u th cng th hin kt qu kh quan khi p dng mc Carbon-nn tng t vo h thng ti tun hon nc lin tc. Mi trng nc thi vi u th thuc v vi khun c c trng bi pH thp v n nh (8.0-8.2) cng nh mc Oxy ha tan thp hn (trong khong 6.9-8.8), sinh khi cao hn v t l thc vt ph du thp hn mc thng thng. iu ny cho thy cht lng nc thi sau khi qua x l vi ao bio-floc hon ton c th ti s dng c. Mt s h thng nui ci tin (kt hp h thu cht thi v ao x l bio-floc) cng c thit k da trn cc kt qu nghin cu thu c. Kt qu th nghim v cc gii php ti s dng nc thi l c s minh chng v cng thuyt phc kt lun rng phng php x l bio-floc l mt trong nhng cng ngh ha hn nht trong tin trnh thit k v hon thin h thng nui hon ton khng nc thi.


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Gii thiu Mc tiu ln nht ca d n CARD l pht trin mt h thng ao nui thy sn hin i nhm p ng nhu cu nui bn vng v em li hiu qu kinh t cao nht bng cch thit k mi hoc ci tin cc cng trnh nui km hiu qu ang c s dng Vit Nam v c. Trn c s ny, nhiu gii php xut c th nghim v nh gi tnh hiu qu trong vic nng cao sn lng nui v ti u ha qun l sn xut. Trong d n ny, h thng mng ni chi ph thp c thit k v th nghim trong nhiu giai on nui nh ng nui u trng, ng ging v c nui thng phm. Cc kt qu thu c t thc t chng t rng vic p dng h thng mng ni trong NTTS l hon ton kh thi v kh quan. Nh trong bo co s 4 nu, kt qu th nghim dng h thng mng ni trong ao nui thy sn ti Trung tm nghin cu NTTS o Bribie cho thy kh nng sn xut ca h thng ny c th t hn 35 tn/ha tnh chung cho c 2 loi c c v Mulloway. C th thy rng vn c hu ca mi h thng ao nui thy sn l s tch t cc cht thi hu c (phn ln l t thc n tha v cht thi ca vt nui) cng vi cc hp cht Nit v c c c tnh cao i vi thy sinh vt (c bit l ammonia). Ngay c cc qui trnh tt nht hin hnh cng khng th trnh khi vn ny v tm c ch hp thu trung bnh khong 25% lng thc n m chng tiu th vo c th, 75% cn li s c c th sinh vt thi ra mi trng nui ch yu di dng Ammonia (Boyd & Tucker 1998; Funge-Smith and Briggs 1998; Hargreaves 1998). Cc cht thi hu c ny l ngun dinh dng cho thy sinh vt v ty theo mc hu c khc nhau trong nc m s gy ra hin tng n hoa ca to. Mt s nh khoa hc cho rng mc hu c trong ao nui tng ng vi mt nui vo khong trn di 5 tn/ha l mc dinh dng tt nht cho h thc vt ph du (Avnimelech 2003; Brune et al. 2003). Mt to ph du qu cao c th gy bin ng pH mnh v tiu hao Oxy ha tan rt ln, thm ch c th n mc gy cht vt nui. Thng thng, mt to pht trin qu mc n n hoa th sau khi to tn s to ra nhiu ammonia gy c trong mi trng nc (Krom et al. 1989; Boyd 1995; Boyd 2002; Ebeling et al. 2006). Hin thi, bin php thng dng v hiu qu nht hn ch to tn v m bo cht lng mi trng ao nui l thay nc. Tuy nhin, t gc s dng hp l ngun nc v bo v mi trng th vic thay nc thng xuyn v x nc thi ra mi trng chung ch l gii php tm thi v hon ton khng c ng h. Tt nhin t c nng sut thu hoch 35 tn/ha ni trn, cc d n hin nay vn phi x l hoc tin hnh thay nc cho ao nui. Bin php qun l mi trng nc ph bin vn l s dng a Secchi nh gi tnh trng mi trng nc v thay nc hng ngy (trung bnh khong 10% mi ngy xem Bo co s 4). Nh bit, mt trong nhng mc tiu ban u ca d n l tm hiu nh gi cc gii php hn ch nc thi trong NTTS. Cc gii php ny c chia lm nhiu hng. Gii php u tin l vic s dng rong Harpoon Weed (Asparagopsis armata) nh mt tc nhn hp thu dinh dng; mt gii php khc c ngh l tch bit h thng nui lm hai phn khu vc ao nui v khu vc x l sinh hc; v gii php th ba l nghin cu duy tr mt t l Carbon:Nitrogen ti u m bo qu trnh lc sinh hc ca vi khun. Bo co chi tit sau y s trnh by cc kt qu th nghim thu c


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trong thc t t cc gii php nu trn vi mc tiu tin n thit k h thng nui khng nc thi, ng thi i su vo m t v phn tch tnh hiu qu ca h thng lc sinh hc dng vi khun vi trin vng ng dng cao nht. Gii php 1: H thu cht thi rn t trong ao nui nc chy Tng quan: Hin nhin, vic lm gim ngun dinh dng u vo ca ao nui thy sn s gim bt p lc cho qu trnh x l nc thi bng phng php sinh hc. nh k loi b trc tip thc n tha v cht thi ca c t h thng nui nc chy trc khi cc cht thi ny phn hy vo trong nc ao tr li s ngn nga s nhim hu c u vo do cc cht thi ny gy ra cng nh hin tng khong ha trong sut qu trnh nui. Lng cht rn lng ng trong h thng nui thay i theo t l cho n v hiu qu tiu th thc n ca vt nui. Kh nng thu gom cc cht thi rn ny khng nhng ph thuc vo ng thi dng chy ca h thng nui m cn ph thuc vo vic thit k cu trc ca h thu cht thi. Th nghim s b sau y c thc hin nh gi tnh hiu qu ca vic s dng h thu cht thi trong h thng nc chy nh mt bin php lm gim nhim hu c cho ao nui. Phng php: Mt b cha nc ma bng nha plastic c t ti cng thot ca h thng nc chy vi chc nng nh mt h thu cht thi (Hnh 1). Cc h thu ny thng vi ao nui qua mt vi thu linh hot v c kt ni vi mt my bm c ci t hn gi. Mi ngy 2 ln, my bm s t ng vn hnh ht cc cht thi lng ng vo b cha ca h thng. Sau cc cht thi ny s c tin hnh phn tch mc nhim hu c vi cc thng s chc nng c trng nh Tng cht rn (TS), Nit tng s (TN) and Phospho tng s (TP). Trong sut thi gian th nghim (t thng 2 n thng 10, 2006), nh k hng thng tin hnh thu nc thi ca ao nui ti ng thot nc (c bt li u ng) v tin hnh phn tch cc ch tiu tng t, sau so snh kt qu ny vi kt qu ca cc mu thu c trong nghim thc dng h thu cht thi kim tra nh gi tnh khc bit. Cc ch tiu cht lng nc bao gm: Tng cht rn (TS), Nit tng s (TN) and Phospho tng s (TP), c phn tch theo cc qui trnh phn tch hin hnh ca Phng php chun (American Public Health Association 1989), s dng cc thit b phn tch dinh dng ti phng th nghim ca BIARC.


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Hnh 1. Hnh dng v thit k chi tit ca thit b thu cht thi rn dng trong ao ng nc chy. Mt li chn bng plastic (khng th hin trong hnh) c dng ngn c vo ng. Kt qu v tho lun: Cc phn tch cho thy mt vi khc bit nh v nng gia nc thi thot ra t h thu v nc thi thu trc tip t ao nui - ch qua li th ng thot m khng qua x l lng (th hin trong bng 1). Ch tiu cht rn tng s th hin khc bit r nht, vic dng h thu cht thi cho thy kh nng lng kh hiu qu vi kt qu trung bnh cao hn 16% so vi vic x nc trc tip ch dng li lc n thun. i vi cc ch tiu TN v TP, tuy s khc bit nh hn nhng vn cho thy c hiu qu x l. Tuy nhin cc s liu ny khng th x l thng k c do d liu hng thng ca nc thi trc tip t h thng qu t (v th tch trao i nc qu ln nn mi thng ch tin hnh o c 1 ln) nn ko theo khng th xc nh c mc sai s chun. Mc d vy, cc cht rn l lng c thu gom to thnh mt lp bn dy trong h thu cht thi v nh k ht ra khi ao nui. R rng l b phn thu cht thi ca mng ni hot ng thiu hiu qu, v th khng hn ch c s xm nhp ca cc cht dinh dng vo trong ao. Kt qu ny cho thy h thu cht thi khng hiu qu my trong vic thu gom v loi b cht rn nh k. Tuy nhin, xt v mt x l cht thi th h thng h thu ny vn c kh nng hot ng hiu qu nu c s dng trong mt ao x l tch bit ring vi ao nui. Nh vy trong trng hp ny, y l mt bc u thun li thu gom nc thi c mc nhim cao trc khi chuyn sang bc x l bng h thng bio-floc c cp trong phn tip theo. Mt s h thng thu gom cht thi tng t cng c Koo et al. (1995) th nghim trong ao nui nc chy i vi c tr lai v kt qu bo co cng khng kh


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quan. Vn ch yu l do qu trnh lng cc cht rn l lng trong h thu khng my hiu qu. Kh khn tt yu i vi vic lng bn trong ao nui nc chy l khi cc cht rn lng xung y th ng lc nc vn khng mnh tp trung chng li ti ng thot. Trong lc , nc tc ng vo cc thnh b li to nn dng xoy xo trn lin tc nn cc cht rn khng th i xung h thu c (Van Wyk, 1999). Ngoi ra, c nui trong ao cng l mt nguyn nhn ng k v chng c th sc bn ln v a cc cht thi lng ng ha vo trong nc ln na. Bng 1. So snh cc ch tiu cht lng nc trong nc thi t h thng dng thit b v nghim thc i chng (x nc trc tip, ch dng li chn th ng thot) (s ln thu mu cho mi nghim thc =7*).

Ch tiu Nng trung bnh trong nc thi t h thng nui nc chy (mg/L)

Nng trung bnh trong nc thi t h thu cht rn (mg/L)

Tng cht rn 15.4 18.35 Tng Nit 2.07 2.33 Tng Phospho 0.78 0.83

* nh k thu mu v phn tch nc hng thng. Gii php 2: nh gi hiu qu x l nc ca Harpoon Weed Tm tt: tng s dng rong bin nh mt tc nhn sinh hc nhm hp th cc cht thi hu c ra khi ao nui thy sn kh quen thuc vi cc nh khoa hc, tiu biu l bo co tng quan ca Neori et al (2004) m t chi tit v tng i y v cng ngh ny. Hin nay, hai loi rong bin ph bin nht c ch v nghin cu nhiu trong ng dng lc sinh hc l rong xanh thuc ging Ulva v cc loi rong thuc ging Gracilaria. Tuy nhin, thc t cho thy hu ht cc h thng lc sinh hc s dng rong bin u khng c tnh hiu qu v mt kinh t, ch yu do gi thnh ca rong bin qu thp trong khi li cn nhiu lao ng v din tch sn xut tng i ln. Mt s tr ngi khc ca vic nui trng rong bin t nc thi ca ao nui thy sn bao gm nguy c nhim bnh cao (Friedlander et al., 1987), s xm nhp ca ch hi nh amphipods, v cnh tranh dinh dng bi thc vt ph du trong ao nui (Palmer 2005). Hn na, cc cht l lng trong nc thi t ao nui c th tch t trn b mt ca rong bin. Do , kt qu thc t cho thy tc tng trng ca rong bin (v gi tr tng ng ca chng nh mt tc nhn hp thu dinh dng) thng b hn ch rt nhiu v hiu qu lc sinh hc thng thp hn so vi cc kt qu t c trong iu kin th nghim (Palmer 2005; cc kt qu nghin cu trc ca BIARC). D n CARD xut yu cu nh gi kh nng x l cht thi t h thng mng ni nui c bng rong Asparagopsis armata (cn gi l Harpoon Weed). xut ny da trn c s mt nghin cu mi y ca Schuenhoff & Mata (2004) cho thy loi rong ny rt giu cc cht hu c vng thm. Khi c tch chit, cc cht ny s c s dng lm cht chng bm bn hoc thuc dit nm trong m phm. Ngoi ra


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kh nng x l ammonia ca loi rong c phn b t nhin Australia ny cng hn hn mt i tng truyn thng khc l Ulva (Hnh 2).

Hnh 2. Rong Asparagopsis armata mc trn cc bi ngm vnh Moreton, S.E. Qld. nh do Marine Botany Group, University of Qld (2003) cung cp. cng nghin cu c xy dng thu thp rong t vnh Moreton Bay v nh gi tc tng trng, kh nng hp th cc mui dinh dng ca n khi tip xc vi ngun nc thi t ao nui c s dng mng ni ti BIARC. Rong giai on bo t 4, giai on c cho l c kh nng lc sinh hc tt nht. D n tin hnh nhiu t thu mu chung vi cc nh nghin cu v thc vt ca i hc Queensland v ch tm c mt s t rong giai on bo t 4. S rong ny c chuyn v trng trong b ti BIARC vi nc thi t ao nui c s dng mng ni nhm mc ch nhn ging phc v cc th nghim qui m. Tuy nhin, s rong ny b cht khng r nguyn nhn. Da trn nhng kinh nghim m BIARC c v rt nhiu kh khn gp phi trong qu trnh tm kim, thu thp v trng loi rong ny, chng ti quyt nh tm dng cc th nghim s dng rong trong khun kh ca d n CARD. Vic ny s c thc hin mt cch k lng hn qua mt nghin cu x l cht thi NTTS bng phng php sinh hc khc ca BIARC. Cn c trn nhng kt qu nghin cu ca BIARC v vic s dng rong x l sinh hc nc thi chng ti thy s dng rong mt cch hiu qu trong h thng x l th cn phi gim thiu lng thc vt ph du v cc cht rn l lng c trong nc thi, ng thi chuyn cc cht hu c sang dng mui dinh dng m rong c th hp th c. Hin ti BIARC ang c mt d n khc thm d kh nng s dng cc b lc ct c giun nhiu t lm cng vic ny (Palmer 2007). Gii php 3: X l nhim hu c bng vi sinh. Tng quan: Hin nay, ngy cng c nhiu kin ng h vic chuyn i t nhm sinh vt t dng (thc vt ph du) sang s dng nhm sinh vt d dng (ch yu l cc nhm vi sinh vt) x l cc cht thi hu c tn ng ca ao nui thy sn v


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chng thun li hn v hiu qu hn trong vic ti s dng nc. Cc h thng x l nc thi dn dng t lu dng vi khun x l cht thi hu c nh h thng bn hot ha (Arundel 1995). Nhiu nghin cu gn y cho thy cc h thng x l cht thi dng l lng, ni m cc qu trnh d dng chim u th, c tim nng ng dng rt cao trong vic hn ch thay nc cho cc ao nui tm c thng phm (Avnimelech 1999; Burford, et al. 2003; Erler et al. 2005). Trong nui trng thy sn, thut ng h thng Bio-floc c s dng cho cc h thng x l c h vi sinh vt d dng chim u th. Thch thc chnh l phi xc nh c cch thc kt hp cng ngh biofloc vi h thng mng ni nui c. C 2 gii php c xem xt: dng cng ngh biofloc ngay trong ao nui hoc trong mt ao ring bit ri a nc x l tr li h thng. Hu ht cc nghin cu v cng ngh bio-floc trong NTTS u biofloc pht trin ngay trong ao nui nh l mt ngun b sung protein cho sinh vt nui (Avnimelech 1999; McIntosh et al. 2001; Erler et al. 2005) ngoi mc ch kim sot cht lng nc. Mc d c th tng thm lng thc n cho c, s gia tng ca c v suy gim ca hm lng oxy ha tan do bio-flocs gy nn c th c nhng tc ng xu n c nui. Nhu cu oxy ha tan rt cao ca c qun th vi sinh vt trong ao v c nui trong mng c th khin cho h thng d b mt cn bng v b e da nghim trng trong nhng trng hp mt sc kh, mt in. Cc cht rn l lng hm lng cao c th cn tr hot ng ca mang c v cho php cc vi khun, protozoa, nm pht trin gy bnh cho c nui (Boyd 1994). Ngai ra, khng phi loi c nui no cng c th s dng cc ht cu vi khun ny c bit l cc sinh vt bc cao (khng phi bn n lc). V th m vic xy dng ring mt h thng x l nc thi bn cnh ao nui thng phm s dng mng ni xem ra ph hp hn. Cc mui dinh dng c ng ha di dng sinh khi ca vi khun s c nh k loi b ra khi mi trng nc ca ao x l. Nc ao qua x l c th c a li vo ao nui. Trong khi cc ao lng c s dng ph bin Australia x l nc ca ao nui tm c th mt s nghin cu gn y ti a phng cho thy chng hu nh khng c tc dng trong vic gim thp hm lng nit tng cng, ch yu l do nh hng ca qu trnh ti khong ha v nc thi giu thc vt ph du (Preston et al. 2000; Palmer 2005). Thu hoch thc vt ph du trc tip t nc thi l rt kh khn v thng rt tn km cho ngi nui. Chnh v th m cn thit phi c cc bin php k thut thay th tng cng kh nng x l nc thi. cc ao x l cht thi bng cng gnh Bio-floc (BFP) pht huy hiu qu ta cn phi to c c ch chuyn i qun x sinh vt sng trong nc thi t ch b chim u th bi thc vt ph du s chuyn sang b chim u th bi vi khun. Cc vi khun ny s pht trin, ng gi cc cht dinh dng trong c th chng v dnh kt vi nhau to thnh cc ht c kch thc ln (gi l floc) m ta c th thu hoch c. Ta c th lm c iu ny bng cch iu chnh t l C:N ca c cht. Cc vi khun d dng s dng C hu c nh l mt ngun nng lng kt hp vi N sinh tng hp protein to ra t bo mi (Avnimelech 1999). vi khun c th chuyn nit sang dng protein sng th ngun C phi phong ph. Chnh v vy m vic iu chnh t l C:N l v cng quan trng. Ngi ta lm vic ny bng cch b sung ngun C hu c vo trong ao. V l thuyt th ta phi tnh ton t l C:N cn thit da trn t l ny trong vi khun, hiu sut ng ha C ca vi khun trong ao


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v hm lng nit sinh hc di dng c th s dng c trong nc ao (Hargreaves 2006). Avnimelech (1999) xy dng cng thc tnh ton lng C cn b sung da trn d lng ammonia tng cng (TAN). Vn phc tp l ch TAN khng phi l ngun N duy nht m cc vi khun d dng c th s dng c. Cc hp cht nit v c ha tan (DON) hay nitrite, nitrate cng c ng gp quan trng vo lng nit sinh hc c th s dng c trong ao (Preston et al. 2000) v vi khun d dng mc d a thch ammonia c th s dng thm chng (Jorgensen et al. 1994). V th, lng C b sung, nu ch da vo hm lng TAN c th s khng p ng c nhu cu. Vic xc nh hm lng N sinh hc c th s dng c ti mt thi im nht nh l rt kh khn (c th nh xc nh DON th cn phi thc hin cng tc ph mu v phn tch trong phng th nghim) trong khi xc nh TAN li n gin hn nhiu. Chnh v th ta cng khng th ph nh tnh thc t ca phng php m Avnimelech (1999) xut. Nghin cu ny nhm mc ch iu chnh li lng C b sung bng cch xc nh hm lng TAN nht thi c th ng ha ton b lng dinh dng c trong nc thi. Ngoi ra chng ti cn mun nh gi kh nng chuyn i qun x sinh vt trong ao nc thi c xy ring bit t ch b chim u th bi to sang b chim u th bi vi khun vi lng C b sung xc nh c. Phng php: Mt lot cc th nghim c thc hin ti BIARC trong nm 2006. Nc thi c thu t b phn thu cht thi ca cc mng ni ang nui c c v c Mulloway. R ng (37.5% C) l ngun C iu chnh t l C:N trong c hai th nghim do thnh phn ca n ch yu l ng, tng i r tin v c hm lng nit khng ng k. Th nghim 1 Trn c s tm hiu nh gi tc ng ca r ng hai nng khc nhau x l nc thi trong thi gian 48 gi, 9 b th nghim th tch 3L c s dng. Sau khi bm nc thi vo b, tin hnh sc kh lin tc m bo xo trn nc. Cc b th nghim c t trong ti nhm hn ch qu trnh quang hp ca to vi 3 nghim thc : i chng, R ng 1 v R ng 2. Lng r ng s dng c tnh bng cng thc sau (theo Avnimelech 1999): Cadd = Nww x ([C/N]mic/E) Trong : Cadd l lng C cn dng Nww l hm lng N-sinh hc sn c trong nc. [C/N]mic l t l C:N ca vi khun [thng thng t l ny = 5 (Moriarty 1997; Hargreaves 2005)] E l hiu s chuyn ha C ca vi khun [c qui nh = 0.4 (Avnimelech 1999)] T ta c cng thc rt gn tng ng nh sau: Cadd = Nww x 12.5


11

Theo cng thc ny, chuyn ha 1g N-sinh hc thnh sinh khi ca vi sinh vt th cn dng 12.5 g C. Nh vy nu nng ca r ng l 37.5% C th cn dng khong 33.3 g r ng chuyn ha 1 g N-sinh hc. Dung dch r ng chun c pha sn (100 g r ng/L= 37.5 g C/L) b sung vo cc b th nghim. Nghim thc R ng 1 s dng mt lng C thch hp vi lng Nww = hm lng tc thi ca TAN o c trong nc thi ngay sau c bm vo b th nghim. Nghim thc R ng 2 c lng C b sung cao gp i nhm c on lng nit sinh hc sn c trong nc thi m ta khng tnh ton c. Nghim thc i chng khng dng r ng. Sau khi thm nc r ng, hai mu nc (th tch 50mL, mt mu lc bng mng lc 0.45um, mt mu khng lc) c thu t mi b ti cc thi im0, 3, 6, 12, 24, 48 gi. Hm lng cc mui dinh dng c trong mu c c xc nh, bao gm: nit tng cng [TN], phosphorus tng cng [TP], ammonia tng s [TAN], Nitrate/Nitrite [NOx], pht pho v c ha tan [DIP]), nit hu c ha tan [DON] v pht pho hu c ha tan [DOP]. Phng php phn tch s dng l cc phng php chun (American Public Health Association 1989) c thc hin bi mt my phn tch t ng ti BIARC. S liu th nghim c x l bng phng php thng k sinh hc vi thut ton phn tch lp li trn phn mm Genstat 8th. Th nghim 2 Th nghim ny kim tra hiu qu ca vic chuyn i qun x sinh vt trong nc thi t ch b to chim u th sang ch b vi khun chim u th bng cch b sung mt lng C ph hp c xc nh qua Th nghim 1. Nc thi c bm vo 4 mng xi mng (di 8.6m, rng 2.7m, cao 0.8m vi th tch l 19,000 L). Hai mng c dng lm ao x l theo cng ngh Bio-floc (BFPs) v hai mng dng lm ao i chng s dng cng ngh lng th ng (PSP) (xem hnh 3). Nc thi c gi li trong cc mng ny 2 ngy, tng ng vi lng nc thay khong 20% ca ao nui c vi din tch x l cht thi chim khong 30% din tch c s nui (y l nhng thng s k thut c th ca cc c s NTTS ti Australia s dng ao) v tng ng vi kh nng x l thc t ca h thng x l cht thi. Nc thi chy lin tc qua mng nhm m bo chnh xc ca quan trc.

Hnh 3. B th nghim x l nc thi: bn tri l bng cng ngh Bio-floc v bn

phi l bng cch lng th ng


12

m phng chnh xc phng php lng th ng, chng ti khng s dng thit b sc kh hoc khuy ng nc trong cc mng i chng. Nc thi c dn vo cc mng ny qua ng nha. Trong cc mng BFP, s dng sc kh mnh m bo khuy trn u v ngn nga s hin din ca cc vng ym kh trong mng (hnh 3). C hu c c a vo mng theo t l vi lng ammonia c trong nc thi xc nh c qua phn tch duy tr t l C:N cn thit (c xc nh nh th nghim 1) tng ng vi khong 200 mL dung dch r ng/2 ngy. Hng tun tin hnh quan trc nc x l v khng x l bng b quan trc cht lng nc YSI vi cc thng s c bn nh pH, nhit , mn, DO trong sut thi gian th nghim. Phng php xc nh hm lng cc mui dinh dng, cht rn l lng tng s v chlorophyll a c m t th nghim 1. Cc thng s thu c so snh hai h thng vi nhau. Ngoi ra so snh gia nc cha x l v nc x l trong mi h thng s cho php nh gi hiu qu ca tng h thng mt. Cc thay i v cht lng nc c x l bng thng k sinh hc trn phn mm Genstat 8th s dng thut ton php o lp li. Kt qu: Th nghim 1 Kt qu ca mi phn c m t chi tit cng vi s tng qut chung th hin trong hnh 4. Nitrogen Ch tiu TAN trong nghim thc i chng tng ln ng k (p>0.01) trong sut thi gian th nghim. Ngc li, ch sau 3 gi k t khi a ngun C vo nc ao, mc TAN trong c hai nghim thc R ng gim hn 35% so vi ban u v thp hn hn so vi nghim thc i chng (P>0.01). Sau 6 gi tc ng, TAN gim n 65% v rt n nh c 2 nghim thc. Tuy nhin, t 6 gi tr i, mc TAN trong nghim thc R ng 1 li tng tr li, cho thy kh nng tiu hao gn ht lng C cung cp trc khi ammonia c phn hy hon ton. Trong nghim thc c hm lng C b sung cao hn (R ng 2), mc TAN tip tc gim thp (p>0.01) v sau 12 gi k t khi bt u tc ng th 96% lng TAN trong nc c loi b hon ton. Mc TAN bt u tng c ngha (p>0.01) tr li sau 24 gi nghim thc R ng 1 v sau 48 gi nghim thc R ng 2, c th l do s phn hy ca thc vt ph du. Trong khong 3-6 gi u, hm lng DON tng rt cao nghim thc i chng v c gi mc ny trong sut thi gian th nghim. Ngc li, vic b sung ngun C lm chm li s gia tng ca DON hai nghim thc R ng t 6-12 gi Tuy vy 24 gi sau khi b sung C, hm lng DON gim khong 30% nghim thc R ng 1 (p0.05). iu ny cho thy s hin din ca ngun C b sung c th lm thay i qu trnh bin i ca vt cht trong mi trng nhng khng nh hng n hm lng mui dinh dng chung.


13

Hm lng NOx c kim tra nhng u mc rt thp (khng pht hin c hoc khng ng k) trong sut thi gian th nghim. T l C:N cao thng thng s c ch qu trnh nitrat ha v cc vi khun d dng s ln t hon ton vi khun nitrat ha. Phosphorus Din bin ca hm lng DIP theo ng xu th ca TAN. nghim thc i chng DIP tng cao trong sut thi gian th nghim (p>0.01). Tng t, 6 gi sau khi ngun C c a vo mi trng, hm lng DIP n nh 2 nghim thc c s dng r ng (gim khong 50%) nhng sau 12 gi th nghim thc r ng 1 DIP tng tr li trong khi nghim thc r ng 2 DIP tip tc gim n 93% (p>0.01). Hm lng DIP bt u tng tr li sau 24 gi nghim thc r ng 1 v sau 48 gi nghim thc r ng 2. Mc DOP gim mnh (p0.05). Tng t nh vi TN, vic b sung ngun C khng nh hng g n TP trong sut thi gian th nghim.

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 6 12 18 24 30 36 42 48

HOURS

TAN

mg/

L

ControlMolasses 1Molasses 2

0.0

0.1

0.2

0.3

0.4

0.5

0 6 12 18 24 30 36 42 48Hours

DIP

mg/

L


0

2

4

6

8

10

0 6 12 18 24 30 36 42 48HOURS

DO

N m

g/L


0.0

0.5

1.0

1.5

0 6 12 18 24 30 36 42 48Hours

DO

P m

g/L

Molasses 2Molasses 1Control

0

4

8

12

16

20

0 6 12 18 24Hours

TN m

g/L


0.0

1.0

2.0

3.0

4.0

5.0

0 6 12 18 24Hours

TP m

g/L


Hnh 4: Hm lng mui dinh dng trong thi gian th nghim nghim thc i chng v 2 nghim thc s dng r ng (Molasses 1 v Molasses 2)


14

Th nghim 2 Cc thng s chun Cc h thng lng th ng do thc vt ph du chim u th c c th bi pH cao (>8.5) v hm lng DO cao (


15

C 2 c im ca h thng BFP gii thch v s gia tng ca cc mui dinh dng. Trc ht BFP duy tr s l lng v tiu ha cc cht hu c. Th hai, s hnh thnh ca cc khi ht vi khun (gi l floc) khin cho TN v TP tng cao. Do hm lng ca DON cao hn (p


16

Hnh 6: Mc dinh dng trong thi gian th nghim trong nc thi cha x l v

trong h thng BFP v PSP. TSS, mt thng s khc i din cho sinh khi ca ct nc, cho thy xu hng gia tng sinh khi trong h thng BFP (p


17

qu x l ca h thng. Kt qu nghin cu ca chng ti cng cho thy C tham gia vo qu trnh chuyn ha ca DON. Tuy vy, cn c nhng nghin cu b sung khng nh pht hin ny. Th nghim tip theo s dng C vi hm lng cao hn khng nh tc dng ca n ln mt h thng x l nc thi c nc chy lin tc m thc vt ph du chim u th. Hm lng C cao v cc iu kin thun li pht trin biofloc chuyn h thng sang h c qun x vi khun chim u th. Qun x vi khun ny c cc c th sau:

o Cng quang hp thp th hin qua pH thp v n nh hn (do s phng thch ca CO2 vo trong tng nc) v hm lng oxy ha tan thp (do vi khun s dng oxy ha tan) (Hargreaves 2006).

o Hm lng mui dinh dng cao (Burford, Thompson et al. 2003) o Giu vt cht hu c (c th o lng c qua cc thng s nit v pht pho

tng cng (Avnimelech 2003; Ebeling, et al. 2006). o Hm lng cht rn l lng cao v t trng thp ca to trong sinh khi chung

(Burford et al. 2003). S chuyn i ca h thng t t dng sang d dng c th hin thng qua s khc bit ca cc thng s DO v pH. Cc thng s ny u thp hn h thng d dng (BFP) so vi h thng t dng (PSP). C hai h thng u duy tr cc thng s mi trng quan trng trong khong ph hp v sinh hc, p ng c tiu chun ca C quan Bo v Mi trng (EPA) trong sut thi gian th nghim. Bin php b sung ngun C gim pH c tho lun trong nhiu cng trnh nghin cu (Pote et al. 1990; Avnimelech 2003). Nghin cu ca chng ti khng nh tnh xc thc ca bin php ny nh hiu qu tng t ln DO and pH bng cch a r ng vo h thng BFP. Trong NTTS, vic m bo tnh n nh ca mi trng nui c coi l yu t quan trng hng u (DPI&F 2006). Nghin cu ny cho thy h thng BFP va m bo cht lng nc, va duy tr c s n nh cn thit ca n. C hai loi qun x c to v vi khun chim u th u ng ha cc mui dinh dng ha tan. S suy gim v hm lng ca cc mui dinh dng trong c hai h thng ca nghin cu ny khng nh iu . Tuy vy, h thng BFP t ra hu hiu hn trong vic x l TAN v NOx, u l nhng cht gy c tim nng i vi sinh vt nui. c tnh ca NH3 dng t do ph thuc vo pH v nhit (Hargreaves 1998). V th m hm lng TAN thp cng vi pH thp hn ch c nguy c b nhim c NH3 t do trong h thng BFP. NO2- cng l mt cht c tim nng v c th tch ly khi qu trnh nitrat ha din ra khng han ton (Hargreaves 1998). S suy gim r rt ca NOx (Nitrate+Nitrite) so vi hm lng ca chng trong nc thi khng qua x l cho thy trong h thng x l bng biofloc (BFP), qu trnh ng ha ln t qu trnh nitrat ha. ng ha loi b s hin din ca NOx v ngn cn qu trnh nitrat ha. Nghin cu ny trnh din tim nng s dng cng ngh biofloc x l nc thi trong mt h thng nui tun hon. Chng ta hon ton khng cn phi x thi nc thi ny vo mi trng v phng php trn gip loi b cc cht c hi c trong nc. Nh vy m hm lng TN v TP cao trong ao nui khng cn l mi quan ngi cho sc khe ca ng vt nui. Trong khi th c TAN and NO2 u thp m vn m bo hm lng DO cn thit. Lng cht rn l lng cao c th nh hng n sc khe ca c nui nh bn lun phn trc v th m ao x l bng cng


18

ngh biofloc phi nm tch bit khi ao nui. m bo hiu qu cao nht, cn c bin php tch lc nc khi c bm tr li ao nui c nhu cu oxy sinh hc (BOD) v hm lng cht rn l lng thp. Schneider et al. (2007) cng c kt lun tng t khi th s dng mt l phn ng vi khun x l nc thi trong h thng nui tun hon. Thit b lc ly flocs ny cn phi c nghin cu mt cch c th nhng trc mt c th s dng mt b lc c nh li lc hoc thng lc. Hnh 8 m t phc tho mt h thng nui tun hon c ao x l cht thi bng cng ngh biofloc c s dng nui tm hoc mt i tng n mn xc hu c tn dng cc sn phm giu dinh dng ny v gip cho cc ht vi khun lun l lng trong nc.

Hnh 8. Phc tho thit k h thng tun hon ti s dng nc vi ao x l bng cng ngh biofloc c xy ring

Kt lun Kt qu cc nghin cu thc hin cho thy cng ngh biofloc nu c dng nh mt phn c lp ca h thng tun hon ti s dng nc l cng ngh ha hn nht cho s hnh thnh ca mt h thng nui khp kn, khng x thi ra mi trng. Li cm n Bo co ny trnh by mt phn thng tin ca D n Nui thm canh c bin trong ao bng mng ni - CARD VIE 062/04 do chng trnh Hp tc Pht trin v Nghin cu Nng nghip ti tr thng qua B Nng nghip v Pht trin Nng thn ca Vit Nam. Chng ti xin chn thnh cm n Queensland Department of Primary Industries and Fisheries, c bit l Adrian Collins, Ben Russell v Blair Chilton cho nhng n lc xy dng d n ban u ca h. Chng ti cng cm n cc i tc nghin cu pha Vit Nam do TS. Hong Tng (Gim c Trung tm Nghin cu v o to Quc t, Trng i hc Nha Trang) ch tr v nhng s gip v ng h quan trng trong sut thi gian thc hin d n ny.

Li chn My sc kh F7

hoc tng t cung cp O2 v xo trn nc

X cn loi bn nh k

Tm Bc Th nui mt thp v khng dng thc n b sung tm n to v cc khi ht vi khun (floc)

Nc sch tng mt c ti s dng cho ao nui

Qut nc

Ao nui Bio-floc Pond

Nc thi giu cht hu c t ao nui c bm sang ao x l biofloc

H thng mng ni

Cp nc b sung, b vo lng nc bc hi


19

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Hari, B., B. Madhusoodana Kurup, et al. (2006). The effect of carbohydrate addition on water quality and the nitrogen budget in extensive shrimp culture systems. Aquaculture 252(2-4): 248-263.

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21

Kt hp nui tm S v ng ging c bin trong ao khng thay nc

Hong Tng1*, Michael Burke2, Bnh Th Quyn Quyn1 & Daniel Willett2

1 Trng i hc Nha Trang, Vit Nam. Email: [email protected]

2 Department of Primary Industries and Fisheries, Queensland, Australia.

TM TT

M hnh nui tm S mt thp kt hp vi ng thm canh con ging c bin

bng mng ni trong ao c xy dng v th nghim. Kt qu cho thy cht

lng nc ao tt v n nh trong sut 4 thng nui khng thay nc vi nhiu t

ng ging c Chm, c M v c Gi. Tm nui t kch thc ln v c h s s

dng thc n cao. Cc kh khn pht sinh nh s tht thot ca c ng trong mng

vo ao, Artemia sinh khi khng pht trin c trong ao cha v trc trc ca h

thng cp kh cng c xc nh v c hng khc phc. Nghin cu ny t nn

mng quan trng xy dng mt m hnh nui kt hp theo hng bn vng, cho

php ti s dng nc trong ao nui loi tr cc tc ng mi trng c th ca

ngh nui trng thy sn.

T kha: nui kt hp, c bin, tm, x l sinh hc.

1. M U

Th nghim ng con ging c Chm (Lates calcarifer) c ln bng mng ni

SMART trong ao nui tm c thc hin thnh cng ti Khnh Ha trong khun

kh ca D n Nui thm canh c bin trong ao bng mng ni CARD VIE062/04

(Hoang et al. 2007). Mc d mc tiu c bn ca d n l gp phn gia tng sn lng

con ging c bin c ln v m hng tn dng cc ao nui tm b b hoang t

c, vic xy dng mt m hnh nui khng thay nc hn ch s ly lan ca

bnh dch v cc tc ng xu c th ln mi trng l ht sc cn thit.

Khi c Chm c ng trong mng ni, cht thi ca c v thc n tha c

dng nc a ra khi mng vo ao cha. Vic loi b cc cht thi ny da vo

cc qu trnh chuyn ha vt cht t nhin nu trong ao cha khng c cc i tng

n mn xc hu c. Cc mui dinh dng hnh thnh s c to s dng mt phn.

Phn ln cn li s tch t trong bn y ca ao. Hn ch ln nht ca m hnh ny l


22

ch lng cht thi t mng vo ao khng n nh (m thay i theo v ng)

khin cho cht lng nc trong ao d bin ng do to pht trin mnh ri tn li v

thiu mui dinh dng.

Nghin cu ny s dng Artemia tn dng cc vt cht hu c thi ra t

mng ni. V l thuyt, vic hnh thnh ca mt qun th Artemia trong ao s em

li nhiu li ch khc na. Nu c nui dng tt th c Artemia trng thnh v

con non u s c h thng nng nc bm vo trong mng. C ng nh th

c th tip cn c vi mt ngun thc n sng b dng vi nhiu kch c khc

nhau. Tuy nhin, c th duy tr n nh ngun dinh dng cho to pht trin (cng

l thc n ca Artemia), chng ti la chn phng n th nui tm S (Penaeus

monodon) mt thp. Khi c nui trong ao vi mt t 5 15 con/m2, tm

S thng ln nhanh, t kch thc ln khi thu hoch v v th c th bn vi gi

cao. i tng nui ph ny do c th to thm thu nhp cho ngi ng c.

Lng thc n nh a xung ao hng ngy v cht thi ca tm s gip duy tr

ngun dinh dng nht nh cho to trong ao nui. Nh cht lng nc s c

ci thin (Hoang et al. 2007b).

Bo co ny trnh by thit k ca m hnh v nhng kt qu ban u m chng

ti thu c khi nui tm S Penaeus monodon trong ao cha kt hp vi ng

ging cc i tng c Chm (Lates calcarifer), c M Malaba (Epinephelus

malabaricus) v c Gi (Rachycentron canadum) s dng mng ni l nhn t sn

xut chnh.

2. VT LIU V PHNG PHP 2.1 Thit k m hnh Th nghim c tin hnh trong mt ao nui ven bin c din tch 2000-m2,

nm cch m Nha Phu (Khnh Ha) khong 1 km (Hnh 1). Bt nha c s dng

to vch ngn gia ao, hnh thnh dng chy trn trong ao khi vn hnh my qut

nc cng sut 2 HP ca i Loan. Qut ny c vn hnh 4 gi mi ngy, t 05:00

07:00 v t 15:00 17:00. Su mng ni SMART-1 (th tch 3 m3/mng) v mt

mng ni SMART-2 (th tch 6 m3) c t mt u ao (Hnh 2). C c ng

trong cc mng ny ln kch thc ln hn. Tm S v Artemia c nui trong ao

cha. Li chn mt mng c dng ngn nga c Chm ng trong mng

xm nhp vo trong ao tr thnh ch hi cho tm nui.


23

Hnh 1: im th nghim. Ao th nghim pha bn tri (du mi tn)

Hnh 2: Mng ni SMART-1 (tri) v hot ng ci to ao (phi)

Trc khi tin hnh th nghim, ao cha c rt cn nc v phi nng 7 ngy.

Tip theo vi nng nghip c ri u mt y ao vi liu lng 7 kg/100 m2. Sau

nc c cp vo ao t mng dn v lng 3 ngy trc khi x l bng

chlorine (25 ppm). Mt tun sau tin hnh ko dy xch st trn nn y khuy o,

pht tn mui dinh dng vo trong ct nc, gip to pht trin. Sau mt tun na

th Artemia nauplii vo ao vi mt 5 c th/L lin tc trong 4 tun (mi tun 1 ln).

Cng lc th ging tm S. Cho tm n thc n cng nghip (ca Grobest) t tun

th 2 tr i. 2.2 Ngun tm c ging C Chm ging c 20 mm chiu di ton thn c mua v vn chuyn trong ti

PE ng oxy vi mt 500 con/ti (5 L). C ging khe v khng c bt c du hiu

bt thng g. Trc khi vn chuyn, c c lc phn c m bo s ng

u. Thi gian vn chuyn khong 1 gi. C c thun cho quen vi nhit nc

ao trong khong 30 pht ri th vo mng ni.

C M Malaba (Epinephelus malabaricus, chiu di tng cng 5 cm) v c Gi

(Rachycentron canadum, chiu di tng cng t 2 10 cm) c sn xut nhn to


24

min Ca L v Ct B v vn chuyn nhiu t bng ng b vo Nha Trang. Mt

vn chuyn l 2.000 con/b (500 L). Nc trong b vn chuyn c duy tr trong

khong 22 23oC v sc kh lin tc. Trong sut qu trnh vn chuyn (24 gi) khng

tin hnh thay nc. Khng cho c n 24 gi trc khi vn chuyn.

Tm S ging PL15 (Penaeus monodon) mua t tri ging a phng c kim

tra bnh bng phng php PCR. Kt qu cho thy tm mnh khe, khng nhim

bnh. Tm ging c vn chuyn v im th nghim trong cc ti nha ng oxy

vi mt 1,000 PLs/ti (2 L). Ban u th nghim s dng trng bo xc ca

Artemia thu t Great Lake (USA) lm ngun cung cp nauplii th vo ao nui cho

2 ln th u tin. Tuy vy, sau th nghim chuyn sang dng dng Artemia Vnh

Chu (Vit Nam) cho 2 t tip theo v nghi ng dng Great Lake khng thch ng

c vi iu kin ca ao nui. Vi c 2 dng, trng bo xc c ty trng v lm

mng v bng chlorine 200 ppm trc khi p. Sau khi n 24 gi, Artemia nauplii

c thu v th u vo trong ao.

Hnh 3: Thu mu phn tch cht lng nc (tri) v cho c n (phi)

2.3 Quan trc cht lng nc Cc yu t mi trng quan trng nh nhit nc, pH, hm lng oxy ha

tan (DO) c o c 2 ln/ngy vo lc 06:00 07:00 v 14:00 15:00. Do khng

tin hnh thay nc trong ton b thi gian th nghim nn mn khng thay i

nhiu v ch c kim tra hai ngy mt ln. Hng tun, tin hnh thu mu nc ao

(Hnh 3) v phn tch hm lng NH3-N, NO2-, NO3- v PO43- bng cc b phn tch

nhanh (do c sn xut) thng dng trong nui c cnh.

2.4 Qun l, chm sc v kim tra tc tng trng


25

C ging c cho n nhiu ln trong ngy t 06:30 n 17:30, mi ln cch

nhau 2 gi. Thc n l loi vin ca INVE (Thailand) cho c bin v GROBEST

(Vietnam) cho tm. Thc n vin, chuyn dng cho c bin ca INVE (kch thc ht

800 1200 m) ch c dng trong tun u tin do lc ny c i hi thc n c

kch thc nh, u v chm chm. Vi c Chm, y l loi thc n m c ging

quen s dng khi cn trong b ng ti tri sn xut ging. Thc n vin ca

GROBEST (loi dnh cho tm, c 2 3 mm) c dng cho c n t tun th 2 tr i

(Hnh 3). Khong na gi trc khi cho c n, trn thc n vin vi vitamin C v o

bng du mc. Khu phn n hng ngy vo khong 10 18% khi lng thn ca c

v c iu chnh theo nhu cu thc ca c ging cng nh iu kin thi tit. Kch

thc, khi lng thn ca c khi bt u v kt thc th nghim c o c v ghi

chp li. theo di tc tng trng ca c, nh k thu mu ngu nhin 30 con

hng tun.

Tm c cho n 2 ln/ngy vo lc 09:00 v 18:00. Khu phn n hng ngy l

10% sinh khi tm nui trong thng u v 5% cho 3 thng cn li. Thc n vin cho

tm c ri u khp ao kt hp vi kim tra hai nh cho n. Sc khe ca tm c

theo di bng cch kim tra tm trong nh cho n v khi tm ln bng chi.

3. KT QU 3.1 Vn chuyn c Vi c Chm vic vn chuyn khng c g kh khn do qung ng vn chuyn

t tri ging n ni th nghim ngn. Do con ging c M Malaba v c Gi khng

c a phng chng ti tin hnh vn chuyn c ging t Ca L v Ct B v

Nha Trang. di ca qung ng l 1.000 1.400 km v phi mt n 24 gi hoc

hn a c v n ni. Nhn chung, kt qu vn chuyn c M Malaba tt hn c

Gi rt nhiu. T l cht trong vn chuyn thp hn 5%, ch yu l do c i n nhau

trong qu trnh vn chuyn vi mt cao. C bt mi ngay khi v n a im th

nghim.

Mt vn chuyn (2.000 con c M 4 cm hoc c Gi 5 cm, 1.000 con c Gi

10 cm trong b cha 400 L nc bin sch) p dng t ra ph hp. Mc d khng

c cho n 24 gi trc khi vn chuyn, c vn nn thc n cha tiu ha ht vo

nc b v cng vi cht thi ca chng lm cho cht lng nc trong b vn

chuyn xu i. Hin trng ny cho thy cn phi thit k cc b vn chuyn c trang

b h thng lc n gin c th nhanh chng loi b cc cht thi ny. Probiotics


26

cng nn c s dng loi tr NH3. Nhit nc c duy tr trong khong 22

24oC t ra rt thch hp vi c M Malaba v c Gi ging. C Gi nhy cm vi

nhit nc v hm lng oxy ha tan hn l c M Malaba. Chng tr nn km

linh hot v c t l hao ht cao hn khi nhit gim xung c 20oC. Chng ti

th vn chuyn c 20 ngy tui (c chiu di ton thn khong 2 cm) hai mc nhit

22 24oC v 26 27oC. Kt qu cho thy ton b c vn chuyn mc nhit

thp hn cht sau khong 3 4 gi. mc nhit cao hn, t l sng l 42% sau

24 gi vn chuyn nhng c rt yu, c th do nhng tn thng c hc v i.

3.2 Kt qu ng c ging Tng cng c 7 t ng c thc hin (2 cho c Chm, 2 cho c M v 3

cho c Gi) trong thi gian th nghim l 4 thng. C pht trin tt trong mng

nhng t l sng c khc bit ln gia cc i tng (Bng 1, 2). Cng ging nh cc

th nghim trc thc hin, c Chm ging 2-cm t kch thc 4 5 cm ch sau 2

tun v 6 8 cm sau 3 tun nhit nc 29 31oC. T l sng thay i ty theo

t ng, t 51 n 78 % v c lin h mt thit vi cht lng v ng u ca

c ging. C Chm dng cho t ng th 2 c mua t RIA3 khng c u v

kch thc. V th t l hao ht trong tun u tin l kh ln khin cho t l sng ca

ton t ch t 51%, thp hn so vi mc k vng.

Bng 1: Kt qu ng c Chm v c M Malaba trong mng ni

C Chm C M Malaba Cc thng s

t 1 t 2 t 1 t 2

C th (cm) 2,0 0,1 2,3 0,8 5,2 0,4 6,3 0,5

C thu hoch (cm) 6,2 1,1 8,4 1,0 11,0 0,7 6,9 0,4

Thi gian ng (day) 23 41 41 10

Tc tng trng

(cm/ngy)

0,182 0,149 0,141 0,086

S lng c th 30,000 20,000 2,000 5,000

S lng c thu 23,400 10,202 1,921 4,960*

T l sng (%) 78,0 51,0 96,0 99,2*

*s liu vo ngy th 7 ca t ng, 2 ngy trc khi c cht do bo lm hng h thng dn kh

vo ngy 05/08/2007


27

Bng 2: Kt qu ng c Gi

Cc thng s t 1 t 2 t 3

C th Chiu di (cm)

Khi lng (g)

5,1 0,3 10,9 1,1

7,7 2,1

9,0 1,0

C thu hoch Chiu di (cm)

Khi lng (g)

10,2 1,6

4,5 2,1

51,0 16,1

12,3 1,5*

Thi gian ng (ngy) 16 44 10

S c th 4,000 1,000 1,500

S c thu 2,080 582 1,456*

T l sng (%) 52,0 58,2 97,1**s liu vo ngy th 7 ca t ng, 2 ngy trc khi c cht do bo lm hng h thng dn kh

vo ngy 05/08/2007

Hnh 4: theo chiu kim ng h t tri qua (a) cho c Gi ging n, (b) c bt mi

mnh, (c) c Gi khi thu hoch v (d) c M Malaba khi thu hoch

C m Malaba pht trin rt tt trong mng ni. t ng th 2 cho thy mt

ng c th tng ln c 5.000 10.000 con/mng SMART-1 nu kinh ph u t


28

sn xut khng b hn ch. C lm quen rt nhanh vi thc n cng nghip, c bit l

thc n cho tm ca Grobest sau mt tun c cho n bng thc n vin (c gi rt

cao) ca INVE. T l sng cao v sc khe tt ca c ging khi thu hoch cho thy

chng ta c th ng c M ging bng thc n vin sn c trn th trng v c th

gim chi ph ng v gi ca thc n cho tm ca Grobest ch bng 1/5 gi thc n

vin cho c bin ca INVE. Loi ny, tuy vy, vn rt cn thit cho c trong tun u

tin v c hm lng cht dinh dng cao, ng u v kch c v c ni tt.

Kt qu thu c vi c Gi km hn so vi c Chm v c M. C bt mi tt,

ln nhanh. Tuy vy t l sng khng cao, c bit l vi 2 t ng u. Quan st cho

thy c c th b nhim k sinh trng (gi l k sinh trung ma xun, Nguyn

Quang Huy - RIA1) do chng b nhim ti tri sn xut ging trc khi chuyn v

a im th nghim. C c sng v c cht u c chuyn n phng th

nghim ca B mn Bnh hc Thy sn (Trng i hc Nha Trang) kim tra.

Tuy nhin, khng c kt lun r rng v nguyn nhn gy cht hoc tc nhn gy

bnh. Chng ti tin hnh tm cho c bng nc ngt (theo hng dn ca ng

Nguyn Quang Huy RIA1) v hn ch c mt phn t l hao ht ca c. C Gi

ng vn cht ri rc hng ngy. Nhng con c nhim bnh bi li chm chp trn

mt nc, b n v mang ca chng b thi ra. Ngoi ra khng c du hiu g khc.

C cht sau khong 3 4 ngy t khi c du hiu b bnh v rt gy do b n.

Hnh 5: C Gi ging cht c mang b thi ra

Cc t ng cn cho thy c Gi rt nhy cm vi hm lng oxy ha tan ca

nc. Sc khe ca c c th b nh hng nghim trng hoc c c th cht ch sau


29

mt thi gian rt ngn c lu gi trong mi trng c hm lng oxy ha tan thp,

i.e. khong 5 pht trong x nha 20 L c cha 150 con c ging. V th m vic vn

chuyn c ging n v t mng ni l rt kh khn c bit sau thi gian ng khi

kch thc ca c ln n 15 25 cm. Vic ng ging c Gi v th nn c tin

hnh cc vng vnh ven bin, c a hnh c che ch khi sng gi. iu ny s

gip loi tr chi ph chun b, ci to ao v chi ph x l v duy tr cht lng nc.

Nu s dng mng ni SMART-2 (t ni, th tch hot ng 6 m3; Hoang & Burke

2007) th ta c th ko c mng ni bng thuyn nh n a im nui thng

phm v vn chuyn c mt cch d dng vo cc lng nui. Quan trng hn, c

ging lun c gi trong mi trng nc, khng b stress v lm quen dn vi s

thay i mi trng sng. Tuy nhin, s dng mng ni ng c t c 4 cm ln

c ln hn vn l mt gii php kh hiu qu.

3.3 Kt qu nui tm S Tm nui c thu hoch sau 114 ngy nui. Tng lng tm thu c l 286

kg. Tm c kch c ln v rt u, trung bnh 29,2 g/con. Kt qu ny tt hn nhiu

so vi cc tri nui xung quanh. Trong thi gian khong vi nm tr li y c th

nui tm t kch thc ny sau 4 thng l rt kh. Nh kch thc ln, tm thu

hoch c c gi bn cao khong 7,86 la c/kg. Tuy vy, t l sng ch t

32,6%, km nhiu so vi k vng (i.e. 75 80% hoc 700 kg) ch yu l do tm b c

Chm thot ra t mng n tht.

Hnh 6: Tm S nui trong ao cha mt thng trc khi thu hoch (tri) v ti

thi im thu hoch (phi)


30

Hnh 7: C Chm (Lates calcarifer) ging thot ra t mng ni tr thnh ch hi

cho tm nui trong ao

Khong 120 con c Chm c ln (110 340 g, nhng con nh hn khng m)

b bt ti thi im thu hoch. Ngoi ra, trong thi gian th nghim chng ti

bt hn 100 con t ao nui bng chi. Tin hnh m mu 10 con cho kt qu 60% c

xc tm trong d dy (Hnh 7). S cn li rut y thc n vin cho tm. Th nghim

s dng tng cng 344 kg nui tm. Hiu sut s dng thc n (FE) v th t

0,83. H s chuyn i thc n (FCR) ca tm, nu c th tnh c s thp hn 1,2

do trong ao cn c c v mt s sinh vt nh khc.

3.4 Phn tch ti chnh Ngoi mc ch n nh mi trng nui th li nhun thu c t h thng nui

kt hp ny cng rt quan trng, c bit khi so snh vi nui n tm hoc ch ng

ging c bin trong ao. Bn phn tch ti chnh ny c thc hin trn c s chi ph

thc t ca th nghim v gi tr ca c ging trn th thng ti thi im thu hoch.

Cn bo m ngy 4 rng sng ngy 5/08/2007 vo Nha Trang lm t ng dn

kh t my thi trung tm n mng ni khin ton b c ging ang c ng

trong mng cht v thiu oxy ha tan trc khi s c ny c pht hin. S c do

thin tai gy ra ny nh hng ln n li nhun k vng t m hnh nui. V th,

chng ta c th xem xt 3 tnh hung khc nhau.

Vi tnh hung 1, gi s c ging ng trong mng c bn ngay trc khi

xy ra s c ngy 05/08/2007 th li nhun ca c t s l A$ 2.737 cho 2.000-m2 ao

hoc tng ng vi A$ 27.374 nu qui i cho 1 ha ao vi 2 t sn xut hay A$

41.061 vi 3 t sn xut mt nm. Trong tnh hung th 2, nu gi tr ca s c b

cht do s c khng c tnh, s tin l s l A$ 1.699 cho t sn xut 4 thng. Tuy

vy, nu vic ngn chn c ging t mng xm nhp vo ao c thc hin mt


31

cch hiu qu, sn lng tm thu hoch c vo cui v s l t 500 700 kg, tng

ng vi gi tr khong A$ 3.930 5.502. Phn gia tng t ngun thu t tm nui s

l A$ 1.682 3.254, hon ton c th b cho s c ca c ng v em li mt li

nhun nh.

Bng 2: Phn tch ti chnh cho m hnh nui vi thi gian 4 thng

Hng mc S lng Gi n v (A$)

Tng (A$)

Chi ph vn hnh thc t Tm ging 30.000 con 0,0021 64,3Thc n cho tm 344 kg 1,57 540,6C ging Chm M Malaba Gi

50.000 con7.000 con6.500 con

2,857,03,000,03,214,3

Thc n cho c INVE Grobest*

2567

15,711,57

392,8105,2

Trng bo xc Artemia 3 kg 80,00 240,0Ci to ao 400,0in, xng du 4 thng 200,00 800,0Cng nhn 4 thng 200,00 800,0Chi khc 300,0

Thu ao 4 thng 100,0 400,0Khu hao h thng mng 4 months 200,0 800,0

TNG CHI 13.714,3Thu nhp

C Chm 5.529,0C M Malaba 5.109,6C Gi 3.565,1Tm S 2.248,0

TNG THU 16.451,7Li nhun/4 thng/2.000 m2 2.737,4

Li nhun qui i cho 1 ha/nm vi 2 v sn xut 27.374,1Li nhun qui i cho 1 ha/nm vi 3 v sn xut 41.061,2

Sau cng, chng ta thy rng th nghim ny mi ch l bc u tin kim

chng m hnh nui kt hp khng thay nc. Qua th nghim cc hn ch c

pht hin v nu thc hin li, chc chn s c khc phc mt cch hiu qu,

m bo li nhun ca h thng. Ni nh th l v cc s c nh c Chm ging t

mng xm nhp vo ao hay h hng ca ng ng kh do bo hon ton c th


32

ngn chn c khi trin khai m hnh ny qui m thng mi do h thng nui s

c thit lp mt cch chc chn hn. H thng nui kt hp khng nay nc ny

chc chn l mt trong nhng la chn m ngi nui tm hoc ng c Vit Nam

c th xem xt v ng dng. Trong thi gian ti cn c nhng nghin cu b sung

hon thin n.

3.5 Cht lng nc ao nui H thng nui kt hp khng thay nc ny c thit k tng cng tnh

n nh ca mi trng nui ni m cc vt cht c tun hon nh vo cc qu

trnh t nhin v sinh hc. Thc t cho thy mc tiu ny l kh d v c tm v c

nui u pht trin tt. Thm vo , hot ng quan trc mi trng h tr thm

cho nhn nh ny (Bng 3).

Tht vng duy nht chnh l d kin nui sinh khi Artemia trong ao cha

khng thc hin c. Trong nhiu nguyn nhn c th ngh n th kh nng Artemia

nauplii b cnh tranh hoc tiu dit bi copepods l kh cao. Do sn phm chnh ca

h thng nui kt hp ny l con ging c bin, vic pht trin qun th Artemia trong

ao nui l ht sc quan trng va cung cp thm thc n sng cho c, va gip

chuyn i vt cht nhanh v d dng hn. cc th nghim tip theo, cn thit phi

tin hnh th ging Artemia ngay sau khi x l nc ao xong v bm to nui sn vo

ao to mu nc, lm thc n cho chng.

Bng 3: Cht lng nc ao trong thi gian th nghim. ND: khng pht hin

c

Thng s Khong bin ng TB S.D.

Nhit (oC) 26,4 36,6 32,4 2,1

pH 7,6 8,6

Bin ng pH trong ngy 0,1 0,7

DO (mg/L) lc 7 gi sng 3,3 6,5 4,9 0,8

DO (mg/L) lc 2 gi chiu 4,2 14,8 9,7 1,7

kim (mg CaCO3/L) 90 110 96 7,0

trng Secchi (cm) 27 55 36,6 7,2

mn (ppt) 28 31 29,2 1,2

NH3-N (mg/L) ND 0,2

NO2- (mg/L) ND


33

Mc d thiu Artemia trong chui thc n d kin, cht lng nc ao nui vn

tt v n nh (Bng 3). Bin ng trong ngy ca pH ch t 0.2 n 0.7, l iu

kin l tng cho tm nui (MPEDA/NACA 2003). C c kt qu ny mt phn l

do lng dinh dng t mng vo ao v t cht thi ca tm nui hay thc n tha

l thp. Cc th nghim trc ca d n cho thy thc n c c s dng rt hiu

qu trong mng ni nh vo thit k ca mng v mt ng nui cao (Hoang et

al. 2007a,b). Mt v sinh khi thp ca tm nui, ko theo lng thc n khng

nhiu, cng gip n nh mi trng. Cc thng s thu thp c v trong cho

thy to trong ao pht trin mc va phi v kh n nh, gip hp th c NH3-N

v NO2-. Cn lu l trong sut c t th nghim nc ao khng h c thay. V

th c th gi h thng nui ny l h thng nui khng thay nc.

3.6 Cc vn qun l Mc d s c bo lm gim ng k mc thnh cng ca th nghim,

nghin cu ny thit lp mt bc quan trng cho s pht trin ca m hnh kt

hp (nui tm mt thp trong ao v ng thm canh c bin trong ao) y ha

hn ny. Th nghim em li nhiu bi hc v cc hn ch u c th khc phc

c khi m hnh ny c ng dng:

Cht lng ca c ging: cn khe mnh, khng nhim mm bnh v

tng i ng u v kch thc. T l sng thp hn d kin ca c

Chm t ng th 2 hay hin tng c Gi cht nhiu trong 2 t

ng u ca th nghim ny l nhng minh chng r rng.

nh k phng bnh cho c: mt trong nhng thun li ca vic s dng

mng ni ng ging c bin chnh l khu phng bnh v cn phi

c pht huy. Vic tm nc ngt cho c Gi hay c M c th c

thc hin mt cch d dng bng cch bm nc ngt vo mng thay v

bt c ra tm trong b cha nc ngt hn ch ti a cc tn thng

hay stress cho c. c bit vi c M khi c bt ra khi mng bng

vt, vy lng ca con ny c th lm m mt nhng con khc lm gim

ng k gi tr thng phm ca c (ngi mua khng mua c b hng

mt). Tng t, vi c Gi c bt ra khi mng tm thng c

biu hin b stress.

Hn ch cc ri ro: cn c bin php ngn nga c ng trong mng

tht thot vo ao cha nc hoc h hng ca h thng cp kh. C Chm


34

c th bi ngc dng v thot ra khi mng ngay ti v tr ca cc ng

nng nc. Ta ch cn bt cc ng ny bng li l c th m bo c

khng thot ra. Bt c h hng no ca h thng cp kh u e da

nghim trng s tn ti ca c ng trong mng. Cn bo u thng 8

tc ng vo ng im yu nht ca h thng l on ni t ng cng

PVC chy trn b vi ng nha mm dn ra mng. Gi mnh vo lc

sau na m y gin mng ra xa hn v ko t mi ni, khin cho

khng kh khng c chuyn vo mng lm c cht ngt. Cn b k

thut, do n np trong nh, khng th can thip kp thi.

4. PHC THO QUI TRNH Phc tho qui trnh ny c xy dng nh l mt hng dn cn bn cho cc c

nhn quan tm mun ng dng hoc p dng m hnh ny. Cc chi tit k thut cn

phi phi c iu chnh cho ph hp vi iu kin sn xut tng a phng v

kh nng u t ca c s:

Kch thc ao: 2.000 m2 vi su ti thiu l 1,2 m. su ca mc

nc trong ao cng ln cng tt. Dng bt plastic phn chia ao lm hai

phn to dng chy trong ao.

Mng ni: Dng mng SMART-1 (3 m3, c gin phao nng ) hoc

SMART-2 (6 m3, t ni) (Hoang & Burke 2007). Tng th tch hot ng

ca c h thng mng c 30 40 m3. Dng mt my nn kh trung tm

cng sut 3 sc nga vn hnh h thng ng nng nc. Cc bin pho

cn thit phi c thc hin m bo tnh chc chn ca h thng ng

cp kh v phi c h thng bo ng khi mt kh.

Chun b ao: tng t nh qui trnh ci to ao nui tm. Khi cp nc

y ao th x l nc bng chlorine (15 ppm). Nn dng phn v c

gip to pht trin v th Artemia xung ngay sau . C th dng mt ti

li ln bao bc tan b h thng mng nhm ngn nga c ging

thot ra ngoi ao v tr thnh ch hi cho tm nui.

Th v nui tm: Mt th tm ging l 15 con/m2. Cn th tm ging

trc khi ng c cng lu cng tt gim thiu t l hao ht ngay c khi

c ging thot c khi mng vo ao v tm ln ln trnh khi ch

hi d hn nhiu. Trong 2 tun u khng cn cho n. T tun th 3 tr i

cho tm n khong 5% khi lng thn/ngy. Tm nui c th t 22 g


35

sau 3 thng v trn 30 g sau 4 thng. Vi mt ao nui 2.000-m2 sn lng

c th t 500 n 700 kg tm nu cht lng nc c m bo v ch

hi c kim sot.

ng c bin trong mng: cc i tng nh c Chm hoc c M

Malaba c th c ng trong mng t c 1.5 cm vi c Chm v 3.0

cm chiu di ton thn vi c M. Nu ng c Gi th cn phi xy dng

v th nghim trc k hoch vn chuyn con ging c ln ra lng nui

thng phm v vic ny tng i kh khn do c rt nhy cm vi tn

thng c hc v hm lng oxy ha tan thp. Mt ng t 3.000

5.000 con/m3 vi c CHm; 1.800 3.000 con/m3 vi c M Malaba. Mt

ng ban u vi c Bp 4 5 cm c th l 1.000 con/m3 nhng cn

phi c gim dn (c bit l v sinh khi) do c pht trin rt nhanh,

i.e. tng 0.6 1.0 cm/ngy. Trong 7 ngy ng u, cho c n thc n

vin ca INVE (800 1,200 m). Khong 3 ngy sau bt u tp cho c

n thc n tm ca GROBEST (2 mm) v cho c n thun ty thc n ny

t tun th 2 tr i. Trc khi n trn thc n vi Vitamin C v du mc

(20 mL cho mi kg thc n) v yn 30 pht trong khng kh cho kh

mt li.

Qun l cht lng nc: cc thng s quan trng nh DO, pH, nhit ,

trong v mn cn c quan trc hng ngy. Hng tun kim tra

NH3-N, kim v NO2-. Mi tun s dng mt ti 500 g ch phm vi

sinh Pondplus duy tr cht lng nc ao.

Qun l h thng: C gng duy tr thng xuyn hot ng ng c bin

trong mng. iu ny gip m bo n nh lng dinh dng t

mng cung cp cho ao, nh vy n nh mc pht trin ca to. Cn

tp trung vo khu nui tm v kinh nghim cho thy y l phng php

hiu qu qun l cht lng nc trong ao nui do hot ng ng c

thng khng lin tc do ngun cung cp hoc nhu cu ca th trng hay

thay i.

H tr k thut: c th tm kim t cc chuyn gia nui trng thy sn

a phng cho ph hp vi i tng nui m bn la chn. Nhng vn

lin quan n mng ni v nguyn l hot ng ca m hnh nui kt

hp ny c th tham kho kin ca Queensland Department of Primary


36

Industries & Fisheries ti Australia hoc B Nng nghip v Pht trin

Nng thn hay Trng i hc Nha Trang ti Vit Nam.

LI CM N

Chng ti xin chn thnh cm n Trung tm Khuyn ng Khnh Ha (KFEC)

nhit tnh gip v cho php chng ti s dng c s vt cht thc hin th

nghim ny. Xin chn thnh cm n cc c nhn KS. Hynh Kim Khnh (KFEC), KS.

Ng Vn Mnh (B mn Nui Hi sn), bn Nguyn Hng Hiu (N45, Trng i

hc Nha Trang), TS. Th Ha v cc cn b ti B mn Bnh hc Thy sn

(Trng H Nha Trang) gip trin khai cc hot ng ca d n. D n ny

chc chn s khng th c thc hin mt cch hiu qu nu thiu s h tr lin tc

ca Queensland Department of Primary Industries & Fisheries (Australia), B Nng

nghip v Pht trin Nng thn, Vn phng Chng trnh CARD v Trng i hc

Nha Trang.

TI LIU THAM KHO

Hoang T., Luu T. P. & Huynh K.K. (2007) Trials of advanced nursing of barramundi

Lates calcarifer in in-pond floating raceways. Journal of Fisheries Science and

Technology 01/07: 12-18 (in Vietnamese).

Hoang T., Huynh K.K., Banh T.Q.Q, Nguyen D.M & Burke M. (2007) Use of

floating raceways for marine finfish fingerling production and potential for the

development of an integrated farming system. In: Proceeding of IMOLA

Symposium, Hue 19 20 April, 2007, pp 1 14. Hue University of Agriculture

and Forestry.

Hoang T. & Burke M. (2007) Floating raceways provide options for marine fish

fingerling production. Global Aquaculture Advocate Jul-Aug: 54-55.

MPEDA/NACA (2003) Shrimp Health Management Extension Manual. Prepared by

the Network of Aquaculture Centres in Asia-Pacific (NACA) and Marine

Products Export Development Authority (MPEDA), India, in cooperation with

the Aquatic Animal Health Research Institute, Bangkok, Thailand; Siam Natural

Resources Ltd., Bangkok, Thailand; and AusVet Animal Health Services,

Australia. Published by the MPEDA, Cochin, India.

Documents

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