Effects of dietary small peptides on growth, serum biochemistry, antioxidant status, and immune responses in juvenile snakehead (Channa argus)

Abstract

The present study was conducted to evaluate the effects of small peptides on growth serum biochemistry, antioxidant status, and immune responses in juvenile snakehead (Channa argus). A basal diet was supplemented with 0%, 1%, 2%, 3%, and 4% small peptides or 2% protein reduction feed for 56 days (SP + , SP-, SP1, SP2, SP3, SP4, and SP-, respectively). The results showed that 2–4% of small peptides had an excellent nutritional gain and were able to maintain and promote the absorption and utilization of protein in C. argus after reducing the feed protein level. Meanwhile, the crude protein content liver gradually increased, crude fat content gradually decreased, and glutamic oxalyl transaminase (AST) and glutamic alanine transaminase (ALT) greatly increased and had the highest value in the SP4 group. The relative gene expression of IL-1β was significantly increased after reducing 2% feed protein, and the intestinal tissue morphology also showed shortening of villi, reduction of villi amount, and large detachment of lamina propria. At the same time, the number of erythrocytes and hemoglobin content of the blood was significantly decreased, and the number of leukocytes and granulocytes was significantly increased. However, after the addition of small peptides, the relative gene expression of IL-1β was significantly reduced. In this experiment, the SP3 group showed high biological activity of lysozyme in the serum, mucus, head and kidney, and spleen of C. argus, while its serum, mucus, and post-attack serum had high antimicrobial activity against Aeromonas hydrophila. The serum complement content of C. argus was also substantially increased by the addition of small peptides. In conclusion, the addition of 2–4% dietary small peptides could maintain the normal growth and greatly improve the immune protection ability of C. argus, in the case of a reduced protein level by 2%, and 3% was recommended as the optimum amount of dietary small peptides addition.