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In the two static tanks, 100% of the water volume was replaced every morning before feeding. In the other four tanks, water was continuously supplied through vertical pipe placed at the circumference of the tank. The water flow was adjusted according to biomass and varied between 10-12 and 20-25 L/min for the 4 and 8 kg/m3 densities, respectively.
In floating cages system (trial II), each cage was stocked with different number of fish, ranging from 250 to 500 fish. Sampling was done monthly and in each sampling the weight and total length of about 5 - 10 % of the population were measured. Feeding was done twice a day. Fish were fed based on appetite.
Results & Discussion
The result of tank trial (trial I) of fish cultured at different stocking densities over a 42-day experimental period is shown in table 3. Figure 1 shows fish growth response after 42 days. The final body weight and daily growth rate of fish cultured at 4 kg/m3 were the highest and significantly higher than those cultured at 2 kg/m3. The final body weight and daily growth rate of fish cultured at 8 kg/m3 were not significantly different from those cultured at 2 kg/m3 and 4 kg/m3. Although there was a significant difference in daily growth rate but no significant difference observed in SGR. There was also no significant difference in FCR of fish cultured at different stocking densities. The survival rate recorded in all treatments was higher than 99 %.
SGR of 1.7 - 2.2 % per day was recorded in this trial. The SGR recorded was comparable to those recorded by AQUACOP (1994) (1.3 - 1.8 % per day) and Lee et al (1994) (1.8 - 2.0 % per day). FCR of 1.5 - 2.0 was recorded in this trial. This was comparable to those of 1.8 reported by AQUACOP (1994).
The result of the trial conducted in floating cages is shown in table 4. Figure 2 shows fish growth response after 3 and 4 month for cage B2 & B4 and A2, A3, A4, B3 respectively. Daily growth rate of 1.4 to 2.1 g/fish/day was recorded. Except for cage IV, the daily growth rate for the rest of the cages was about 1.5 g/fish/day. The SGR of 1.2 - 1.9 %/day was recorded in this trial. The SGR recorded in this trial are comparable to those recorded by AQUACOP (1994) (1.8 - 2.0 % per day), Sakaras (1987) (1.2 - 1.3 %/day) and Roki et al (1995) (1.3 - 1.6 %/day).
The FCR for individual cage was not calculated because the actual biomass in each cage could not be determined because of the mass mortality occurred. Based on the total weight of fish that were able to sell (632 kg) and the amount of feed used (929 kg), it was estimated that the FCR was around 1.5. AQUACOP (1994) reported a FCR of 1.8 when fish were fed with semi-commercial feed.
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