Dietary protein requirement of juvenile American eel (Anguilla rostrata) fed practival diets

Triplicate groups of juvenile American eel were fed to satiation herring meal-based diets containing 35, 39, 43, 47 and 51% crude protein (as fed basis) for 84 days. Data were collected to determine the relationship between dietary protein level and the following response variables: mean weight gain (MWG), specific growth rate (SGR), feed conversion ratio (FCR), nutrient digestibility and nutrient retention. Highest MWG and SGR (P<0.05) were obtained when dietary protein was 47% and 51% with values (mean\ub1SEM) of 14.2\ub10.66 g and 12.8\ub10.61 g for MWG, respectively, and values of 1.20\ub10.04%/day and 1.13\ub10.05%/day for SGR, respectively. Optimum FCR (P<0.05) of 1.17\ub10.05 g feed/g gain was achieved by feeding 47% protein and was significantly better than all other levels. Digestibilities of crude protein and energy were similar among the diets containing 39, 43, 47 and 51% protein with mean protein digestibility of 90.7\ub10.54% and mean energy digestibility of 90.3\ub10.60%. However, digestibility coefficients of the 35% protein diet were significantly lower (P<0.05) at 84.9\ub10.97% for protein and 85.2\ub10.98% for energy. Highest carcass protein gain (P<0.05) of 2.2\ub10.11 g/fish was achieved when feeding 47% and 51% protein, while highest carcass lipid gain (P