Seed production and culture techniques of Genetically Improved Farmed Tilapia (GIFT) in brackishwater environment

摘要

Effects of different levels of salinity on survival, growth and gonadal development of Genetically Improved Farmed Tilapia (GIFT) were studied under laboratory conditions in glass aquarium, for a period often weeks. The initial individual size of theGIFT was 20.23±4.45 and the salinity levels tested were 0, 5, 10, 15 and 20 ppt. The highest survival of 87.5% was found in 0 ppt and the lowest 60.5% in 20 ppt. Though the survival decreased progressively with increased salinity, there were no significant differences (P>0.05) among 0, 5, and 10 ppt (Table 1). Similar to what has been observed in survival, the specific growth rate (SGR %/day) also decreased as of 1.30, 1.24, 1.08, 0.90 and 0.71, respectively, with the increased salinity of 0, 5, 10, 15and 20 ppt. The gonadal development was highest in 0 ppt with a GSI value of 3.75 and lowest of 2.01 in 20 ppt. In the second experiment, gonadal development and seed production performance of GIFT in brackishwater condition were investigated for a period of three months. Each of the three fine meshed hapas of 20 m~2 made from nylon net was placed in a freshwater (0 ppt) and in a brackish water (10-15 ppt) pond of the Brackishwater Station (BS). GIFT of 65 g average weight from a single cohort were stocked into three hapas at a rate of 2 m~(-2). The male vs female ratio was 1:3. The development of gonad was faster with the higher gonadosomatic index (GSI %) of 3.85 % in freshwater condition than that of 2.73 % in brackish water. Within three months ofthe study period, a total of 70,510 and 44,250 GIFT fry were produced respectively, in freshwater and brackishwater conditions. Finally under third experiment, a participatory on-farm trial was carried out to evaluate the production performance of GIFTin monoculture and in polyculture with silver barb in coastal freshwater pond conditions. Nine ponds were selected for three treatment combinations of GIFT monoculture (T_1), GIFT and silver barb polyculture (T_2), and silver barb monoculture (T_3). Theponds have been stocked in April, 05 at a density of 25,000 fry ha~(-1). Fishes were fed with rice bran at the rate of 6% bw day~(-1). In one month culture period, GIFT attained an average weight of 16.27 g in monoculture and 17.23 g in polyculture, against an average stocking weight of 0.37 g. Silver barb reached an average weight of 16.62 g in polyculture with GIFT and 10.01 g in monoculture, against an average stocking weight of 3.79 g.