Effects of dietary protein and energy levels on growth, feed coversion and body composition of spotted halibut Verasper variegatus

A 60-day feeding trial was conducted in a running sea water system to determine the appropriate protein and energy levels in the practical diet for spotted halibut Verasper variegatus (initial weight: 50.0 g) . Nine diets of three digestible protein (DP) levels (41, 46 and 56%) , each with three digestible energy (DE) levels (360, 400 and 440 kcal/100 g) resulting in DP/DE ratios ranging from 98 to 150 mg/kcal, were fed to 20 fish per 200l tank) in duplicate. Weight gain tended to improve with increasing dietary DP level and decreasing dietary DE level, reaching a maximum in the diet (56.7% DP and 379 kcalDE/100 g) containing a DE level of 360 kcal/100 g at a DP level of 56%. Feed efficiency, protein efficiency ratio, energy efficiency and nutrient retention reflected growth response. Hematological characteristics were not affected by dietary DP and DE levels, while serum protein, triglyceride and cholesterol concentrations decreased with increasing dietary DE level at a DP level of 41%, and body fat content increased with increasing dietary DE level at DP levels of 46% and 56%. These results indicate that an increase in dietary DE level has no protein-sparing effect and that a diet with 56.7% DP and 379 kcalDE/100 g, corresponding to a DP/DE ratio of 150 mg/kcal, is optimal for growth, feed conversion and body composition of this fish.