Abstract
A 65-day growth trial was conducted to investigate the dietary protein requirements for Culter mongolicus fingerlings. Isolipidic and isoenergetic diets were formulated with five dietary protein levels (32%, 37%, 42%, 47%, and 52%). Each diet was assigned to triplicate groups of 70 C. mongolicus fingerlings (0.99±0.08 g). The results indicated that weight gain and specific growth rate (SGR) increased with increasing dietary protein levels up to 47%. The activities of intestinal trypsin and lipase were the lowest in the 32% protein and 52% protein groups, while amylase activity reduced markedly in the 47% protein group. These results suggest that different dietary protein levels may cause different transformations of nutrients. The activities of superoxide dismutase (SOD) and lysozyme were not affected by varying dietary protein levels, except for those in the 32% protein group. In contrast, the content of malondialdehyde (MDA) increased with increasing dietary protein levels and reaching a maximum in the 52% protein group, suggesting that MDA accumulation depends on the protein concentration and the potential oxidative stress. Taken together, based on the broken-line analysis of SGR, we recommended the optimum dietary protein for C. mongolicus fingerlings to be 48.97%~49.31%.
Highlights
Deficiencies or excesses of the main dietary components have profound effects on the growth and survival of fish [1]
The present study aimed to evaluate the effect of varying dietary protein levels on the growth and the survival rate of C. mongolicus fingerlings in artificial cultivation
specific growth rate of total length (SGRTL) and SGRBW increased significantly (p < 0.05) when dietary protein levels increased from 32% to 47% and a decreasing trend was observed in the 52% protein group
Summary
Deficiencies or excesses of the main dietary components have profound effects on the growth and survival of fish [1]. Protein accounts for 65%~75% of fish dry-weight, and protein deposition in fish appears to be the main determinant of weight gain [2]. It plays a key role in many biological functions, including structural, enzymatic, transport, immune, and cell signaling [3]. Protein is broken down into smaller molecules in the gastrointestinal tract, which secrete fluids, electrolytes, and digestive enzymes that allow the absorption and utilization of free amino acids [4]. Excessive dietary protein can promote ammonia excretion and increase utilization of energy for amino acid catabolism, leading to water pollution and retarded growth
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