Effect of dietary hydroxyproline supplementation on Chinese perch (Siniperca chuatsi) fed with fish meal partially replaced by fermented soybean meal

As a kind of biologically active molecule, hydroxyproline (Hyp) is abundant in fish meal (FM) but not in plant protein sources. It remains very challenging to replace FM with plant protein sources, particularly for carnivorous fish. This study aims to investigate the effect of dietary Hyp supplementation on Chinese perch (Siniperca chuatsi) fed with FM partially replaced by fermented soybean meal (FSM), with 46% FM as the positive control and 31% FM plus 15% FSM as the negative control. Based on the negative control diet, 0.5%, 1%, 1.5% and 2% of dietary crystal L-Hyp was supplemented to formulate four experimental diets, respectively. Although the replacement of 15% FM with FSM in the feed resulted in a significant decline in growth performance of Chinese perch, dietary supplementation of 1% Hyp could improve the growth performance with high mRNA levels of the gh and igf1 genes. Piecewise regression analysis revealed that a dietary level of 2.27% Hyp could achieve the maximum weight gain rate. With high mRNA levels of orexigenic genes (npy and agrp in the brain, and ghrelin in the gut) and low mRNA levels of anorexigenic genes (pomc and cart in the brain, and leptin-A in the liver), an appropriate level of Hyp could be added to the diet of Chinese perch as a food attractant to promote the appetite and increase food intake. Besides, partial replacement of FM with FSM might promote the deposition of amino acids in the muscle, which may not be affected by dietary supplementation of Hyp. Furthermore, dietary supplementation of Hyp affected the activity of prolyl hydroxylase (PHD) and the mRNA levels of type I collagen regulatory genes and coding genes of three prolyl 4-hydroxylase (P4H) isozymes in the muscle of Chinese perch to some extent. In addition, supplementation of an appropriate level of Hyp could significantly improve the collagen content and muscle quality (hardness, chewiness and springiness) of Chinese perch, which may greatly enhance its edible and nutritional values.