The effects of dietary fat and NFE levels on growing European sea bass ( Dicentrarchus labrax L.). Growth rate, body and fillet composition, carcass traits and nutrient retention efficiency

Abstract

European sea bass (91.5±5.7 g) were randomly assigned to 12 tanks (25 fish/tank) and fed six experimental diets for 224 days according to a 3×2 factorial design [three crude fat levels: 11, 15 and 19% on dry matter basis, dm; 2 N-free extract (NFE) levels: 21.5 and 28.5% dm], with two replicates for each treatment. Daily feeding rate was 0.95% live weight. Final weight (339.9 g) and daily energy (11.78 kJ/fish) and protein gain (200 g/fish) were significantly higher for fish fed diets containing 19% fat. The whole body of the fish fed diets with the highest crude fat and NFE levels had significantly lower contents of moisture and protein and a higher level of crude fat. Body ash and P contents (4.41 and 0.7% wet weight) did not differ among treatments. Gross energy, protein and phosphorus retentions (29.2, 19.0 and 32.6%, respectively) and dressing percentage (89.4%) were not affected by treatments. HSI significantly decreased as dietary fat levels increased, only in fish fed diets with the highest amount of NFE. Liver fat content was significantly greater in the fish fed the highest level of NFE (35.2%) in comparison with those fed the lower level of NFE (26.0%) ( P<0.05). Percentage head and viscera (without liver) significantly decreased while percentage mesenteric and perinephric fat significantly increased with dietary fat content. Fillet percentage was significantly lower (44.1%) in fish fed diets containing 21.5% NFE, compared with those fed diets with 28.5% NFE (44.9%). Moisture decreased and lipid content increased in fillet of fish fed diets with 28.5% dietary NFE level, as dietary fat level increase. The saturated, monunsaturated and n−6 polyunsaturated fatty acids of fish muscle significantly decreased while n−3 PUFA levels significantly increased with increasing dietary fat content.