GROWTH PERFORMANCE OF SEA BASS FRY (DICENTRARCHUS LABRAX) UNDER DIFFERENT SALINITIES

This study aimed to investigate the effect of different concentrations of different water salinity (36, 17, 8, 4, 2 ppt. and salinity level is less than 1ppt.) on growth performance and survival rate (%) of sea bass fry Dicentrarchus labrax. One thousand and two hundred sea bass fry were randomized stocked at twelve indoor tanks; 4 m3  each (two replicate/treatment), with an average initial body weight of (2 ± 0.30 g/fish) at the rate of 100 fish / tank. Fish in each tank were hand-fed with commercial diet (40 % crude protein and 485.582 Kcal GE/ 100 g diet). Fish were fed daily at a rate of 15, 10, 5, 4 and 3% of the body weight daily for the (1:2.2); (2.2:3.84); (3.84:9.2);  (9.20:12.70) and (12.70) g/fish : until the end of the experiment, respectively. The daily allowances were divided into three meals at 8.00 am; 11.00 am and 2.00 pm. Fish were fed six days a week throughout the experimental period (167 days). The daily amount of feed was re-adjusted every two weeks according to the actual fish biomass in the tanks. The highest significant values of growth performance parameters were observed when sea bass fry were reared at salinities 8 and 36 ppt. Weight gain of the other treatments were negatively affected (p <0.05) by water salinity. The lowest growth performance parameter was observed by salinity level less than 1 ppt. The highest FCR (1.64) recorded at 8 ppt. compared with (1.73) at 36 ppt. and worsens (1.91) at salinity level of less than 1ppt. The same trend was observed for protein efficiency ratio and condition factor where sea bass fry D. labrax reared at water salinity 8  ppt. recorded the highest value (1.45 and 1.16), respectively, while treatment 6 (less than 1 ppt. salinity) showed the lowest significant (P<0.05) values (1.31 and 1.01), respectively. No mortality was recorded during the experimental period in all treatments. The economic returns studies showed that the total return and net profit were linked to the prices of the raw materials used in the experiment as well as the marketing prices of the fish produced. Total return and net profit showed that the fish reared at 8 ppt. achieved the highest economic return followed by the 36 ppt. and 17 ppt., while treatment 6 (less than 1 ppt.) showed the lowest economic return followed by 4 ppt. Since the feeding cost of these two treatments is 16% higher than the other treatments, which affected the economic returns. However, when evaluating the situation as a high value fish species (like sea bass) with economic value reared in fresh water, this yield is very favorable in terms of cost compared to the selling price.