Growth performance parameters of European Sea bass (Dicentrarchus Labrax) cultured in marine water farm and fed commercial diets of different protein levels

Objective: To evaluate the growth performance and whole-body composition of growing E. Sea bass cultured in marine water farm and fed commercial fish diets containing 42.3% to 39.60% crude protein (CP) and 17.4 % to 17.8 % fat. Design : Randomized controlled study Samples : Five ponds out of the 8-ponds open marine water farm of 12 Feddans were used. Procedures : Each pond (120 m length x 40 m width x 1.5 m depth) stocked with 5500 growing E. Sea bass of about 25 g initial mean body weight. Fish feeding and management were followed up for 6 months (June to November 2018). Diets (extruded, pelleted, 3- 4.5 mm size of different protein levels) offered once daily at satiation (at 7:00 AM) until October and twice daily during November. Diets offered daily decreased from 4.6% of relative BW of fish at the start of the feeding trial to 1.02% at the last month. Partial replacement of ponds water was maintained daily. The high protein diet (42.3%) fed during the first 2 months, in the second 2 months a 40.42% CP diet was fed, while diets fed in the last 2 months contained 39.60% CP. Fish samples (n=20 from each pond) were collected at the end of each month to follow up growth parameters. Fish samples collected (4 from each pond) at the end of the fourth and the sixth months of feeding trial for whole body composition and morphometric indices determination. Results: Body weight gain increased from 47.06 g in the 1st month to 113.80 g at the last month. Feed consumption increased from 68 g/fish/month to 109.08 g/fish/month. Mean body weight of the Sea bass fish was 496.30 g at the end of the follow up feeding periods. Unexpectedly, feed conversion ratio decreased from 1.44 at 1st month to 1.18 at the end of the feeding trial instead of the marked increase in BW of fish. Feed efficiency ratio increased from 69.21% at the 1st month gradually to 87.5% at the end of the 5th month, with a little decrease during last month, (85.0%) parallel to the decrease in water temperature in November. There was a little decrease in moisture percentage of fish body with increase in fish size (67.8 vs 69.10%) with a little increase in protein content (18.55 vs 17.82%) of the Sea bass whole body composition, also fat content increased from 7.94 to 9.25%. Carcass or dressed fish wt. dressed %, fillet yield % and K- factor markedly improved with increasing the fish size at the end of feeding trial. Conclusion and Clinical relevance: In conclusion, it seems that feeding diets containing about 42 to 40 % protein with 17.6 % fat produced appreciable growth of E. Sea bass fish culturing in marine water farm under the semi-intensive feeding system.