Abstract:A 12-week feeding trial was conducted to evaluate the effects of replacement of fish meal with alternative proteins on growth performance, body composition, and physiological and biological indices of juvenile turbot (Scophthalmus maximus L.). Five isonitrogenous and isolipidic practical diets were formulated to contain graded levels (100%, 60%, 50%, 40%, and 30%) of fish meal (D1~D5); the D1 group was used as the control. A protein blend of four ingredients (soybean meal, peanut meal, stickwater meal, poultry by-product meal = 2:1:3:2) were used to replace the fish meal; subsequently, amino acids were supplemented in the low fish meal diet to obtain similar amino acid profiles to the high fish meal diet. Each diet was randomly assigned to triplicate groups of 30 fish [(initial weight, (53.0±0.2) g)] per aquarium. The results of the survival rate, feed conversion ratio, feed intake, whole body moisture and crude protein, dorsal muscle moisture, crude protein, crude lipid, and ash content did not show any significant differences between any of the groups (P>0.05), whereas the diets with low fish meal content (D4/D5) significantly reduced the weight gain rate of fish compared with the control diet (P<0.05). The condition factor was significantly enhanced in the D2 treatment compared with the D3, D4, and D5 groups (P<0.05). However, the viscerosomatic and hepatosomatic indices were significantly reduced in the D2 treatment compared with the D5 (P<0.05). The dietary inclusion of the animal and plant protein mixture significantly elevated the whole-body crude lipid content (P<0.05). The whole-body ash content in the D5 treatment was significantly lower than the control diet (P<0.05). The essential amino acid compositions of the muscle were not significantly affected by the replacement of dietary fish meal with animal and plant protein mixtures (P>0.05). The dietary inclusion of animal and plant protein mixture significantly elevated serum aspartate aminotransferase and alanine transaminase activities (P<0.05). All the substituted protein diets caused significantly reduced serum cholesterol and low-density lipoprotein cholesterol (P<0.05), but only D3~D5 diets caused a significantly decreased serum high-density lipoprotein cholesterol (P<0.05). The dietary inclusion of animal and plant protein mixture had no strong effects on the total protein content and the alkaline phosphatase content (P>0.05). The replacement of up to 50% of dietary fish meal with an animal and plant protein mixture did not impair growth or reduce the feed efficiency of juvenile turbot.
