THE EFFECT OF DIETARY-PROTEIN LEVEL AND SOURCE ON GROWTH, BODY-COMPOSITION, TOTAL AMMONIA AND REACTIVE PHOSPHATE EXCRETION OF GROWING SEA BASS (DICENTRARCHUS-LABRAX)

Three hundred sea bass (75.8 +/- 5.8 g) were randomly distributed among 12 tanks and fed for 168 days, at 1.0% live weight, with one of 6 experimental diets in a 3 X 2 factorial design [3 protein levels: 44, 49 and 54% crude protein (CP) on a dry matter basis; 2 protein sources: herring meal and herring meal plus corn gluten meal] with 2 replicates for each treatment. Final live weight and relative weight gain were affected by the protein level (P < 0.05) but not by the protein source. The moisture and crude protein of fish increased with dietary protein level while fat and energy contents decreased accordingly (P < 0.05). Fish fed the 44% CP herring meal diet had the highest energy, protein and lipid retention. Total ammonia excretion increased linearly and significantly with the protein level of the diet. Diets containing corn gluten gave lower reactive phosphate concentration in the effluent water than those with herring meal (55.1 vs. 113.9 mg PO4/kg/day).