Reef fish are organisms with the greatest amount of biomass and is a conspicuous organisms and can be found on the coral reef ecosystem. Fish group is the largest of a group of vertebrate animals associated with coral reefs. It is estimated that as many as 7000 species of fish inhabit coral reefs. The purpose of this study was to provide information on species composition and abundance, diversity and uniformity of reef fish in the transitional seasons I used to be known early in the monsoon transition Semak Daun Island, Thousand Islands. While its use is as an information management efforts, conservation and utilization of reef fish. The study was conducted with replicates at each transect patent for 3 times a 1 day (2 days) at 12 stations and 24 observation transects were assumed to represent the North, South, East and West for the two depths, with the observation time of the 2nd -12th May 2009. Data retrieval reef fish using visual census method in estimating reef fish populations. Long transect permanently installed which is 10 meters by 24 transects on 2 (two), while the depth range between 2-3 and 9-10 meters. The results showed that the relationship between coral reef fish communities obtained by the tvalue (3,854)> ttable (13 ; 0.05) 1,812, which means that there is a correlation between the presence of coral reefs on reef fish community structure as evidenced also by the value Asymp Sig which show no relationship between the two variables. Linear regression to predict the abundance of reef fish community structure of present cover coral reef obtained by the percentage rate R2 (coefficient of determination) is 0,905. Formed regression equation is: Y = 8,5*10-15 + 0,056 X1 + 1,198 X2 – 0,501 X3 with the dependent variable Zscore_number of reef types.
