Use of a compound protein source as a replacement for fish meal in diets of large yellow croaker, Pseudosciaena crocea R.

A feeding trial was conducted to evaluate the potential of a compound protein source (CPS) as a replacement of fish meal (FM) in diets for large yellow croaker, Pseudosciaena crocea R. The CPS was made of soybean meal, meat and bone meal, peanut meal, and rapeseed meal (4:3:2:1 in weight) by adding crystalline L-methionine (0.77%), L-lysine (0.95%), and L-isoleucine (0.44%) to ensure the essential amino acid (EAA) contents of CPS diets to reach or exceed those of FM diet. Six isonitrogenous and isoenergetic diets (Diets 1-6) were formulated to contain 0, 9, 18, 27, 36, and 45% CPS replacing 0, 13, 26, 39, 52, and 65% FM protein, respectively. Triplicate groups of 180 fish (initial average 1.88 +/- 0.01 g) were fed diets to apparent satiation by hand twice daily for 8 wk in floating sea cages (1.0 x 1.0 x 1.5 m). The water temperature ranged from 26.5 to 29.5 C, the salinity from 25 to 28 parts per thousand, and the dissolved oxygen content was approximately 7 mg/L during the experimental period. The results showed that specific growth rate (SGR) and feed efficiency ratio (FER) of fish fed Diets 2 and 3 were not significantly different from those of fish fed control diet (Diet 1). However, SGR and FER of fish fed Diets 4-6 were significantly lower compared with control group (P < 0.05). The whole-body proximate analysis showed that protein significantly decreased with increasing dietary CPS levels (P < 0.05), while the whole-body lipid, ash, and moisture showed no significant differences among dietary treatments. Methionine, cystine, and lysine contents of the whole body were significantly influenced by dietary CPS level (P < 0.05), while other EAA contents showed no significant differences. Results of the present study indicated that CPS could replace about 26% FM protein in diets for the large yellow croaker on crude protein basis without adverse effect on growth.