Evaluation of cottonseed protein hydrolysate for replacing fish meal in diets of juvenile tiger puffer (Takifugu rubripes)

Abstract

This study was to evaluate cottonseed protein hydrolysate (CPH) as a replacement for fish meal in diets for juvenile tiger puffer (Takifugu rubripes). A commercial CPH that can be applied on a large scale was chosen for the present study. Five diets containing about 470 g/kg crude protein were formulated with incremental levels of CPH at 0, 30, 60, 120 and 240 g/kg (CPH0, CPH3, CPH6, CPH12 and CPH24) of dry matter to replace fish meal. Tiger puffer (initial body weight: 11.69 ± 0.01 g) were randomly assigned in 15, 200-L tanks and fed twice daily to apparent satiation during the 8-week period. Fish fed diets (CPH3, CPH6, CPH12 and CPH24) containing CPH exhibited numerically higher of growth parameters (final body weight, weight gain and specific growth rate) compared to the control group (CPH0), while no significant differences were observed. Feed conversion ratio and protein conversion ratio showed a linear or quadratic relationship with dietary CPH level, and CPH replaced fish meal up to 78.95 g/kg and 127.13 g/kg respectively without compromising on these two parameters of feed utilization. In the intestine, the expression of pept1 for peptide transport, and the expression of asct2, b⁰at1, b^0,+at, y⁺lat1, snat2 and eaat3 for amino acid transport were down-regulated in fish fed high levels of CPH. For mTOR pathway, the expression of mtor, 4e-bp1 and 4e-bp2 was up-regulated in the liver and down-regulated in the muscle in fish fed the CPH24 diet compared the control group. Substitution of CPH for fish meal in diets reduced dietary taurine concentrations and resulted in lower levels of liver and muscle taurine. The expression of cdo and csd for taurine synthesis, and taut for taurine transport was up-regulated with the increase of dietary CPH. Lipid content of whole body, serum total cholesterol content and lipase activity of intestine decreased with increasing levels of dietary CPH, while liver lipid content was observed to be elevated. In addition, textural parameters of muscle were not significantly affected by dietary treatments. In conclusion, 78.95–127.13 g/kg of CPH was suitable for replacing fish meal in the formulation of feed for tiger puffer. However, low taurine concentration of CPH may be a potential factor limiting inclusion when formulating diets for tiger puffer. When an excess of CPH was added to experimental diets, it reduced feed utilization, caused asynchrony in amino acid absorption of intestine and had a negative effect on protein synthesis.