Effects of dietary marine red yeast supplementation on growth performance, antioxidant, immunity, lipid metabolism and mTOR signaling pathway in Juvenile Tilapia (Oreochromis niloticus)

A 60-day feeding trial was conducted to investigate the effects of dietary marine red yeast supplementation on growth performance, body composition, antioxidant, immunity, lipid metabolism, and mTOR signaling pathway in juvenile GIFT tilapia (Initial weight 21.12 +/- 0.86 g). Five isonitrogenous and isolipidic experimental diets were formulated with graded levels of marine red yeast: 0 % (control group), 0.25 %, 0.50 %, 0.75 %, and 1.00 %. The results showed that different marine red yeast levels significantly increased (p < 0.05) the final weight, weight gain rate, specific growth rate, daily growth index, protein efficiency ratio, and condition factor, while significantly decreased (p < 0.05) the feed conversion ratio, viscera index, and hepatosomatic index. Different marine red yeast levels significantly increased (p < 0.05) the activities of foregut lipase, hindgut lipase, foregut alpha-amylase, midgut alpha-amylase, hindgut alpha-amylase, superoxide dismutase, catalase, glutathione peroxidase, and total antioxidant capacity, while the malondialdehyde content expressed an opposite trend. Different marine red yeast levels significantly increased (p < 0.05) the activities (contents) of lysozyme, alkaline phosphatase, immunoglobulin M, and complement protein 3 in serum. Different marine red yeast levels significantly increased (p < 0.05) the relative expression of phosphoryl inositol-3-kinase, protein kinase B, mammalian target of rapamycin, ribosome S6 protein kinase 1, cholesterol response element binding protein 1, peroxisome proliferator-activated receptor gamma, leptin, acetyl-CoA carboxylase alpha, fatty acid synthase, and glucose-6-phosphate dehydrogenase in liver, while the relative expression of PPAR alpha, carnitine palmitoyl transferase 1, lipoprotein lipase, and hormone sensitive lipase expressed an opposite trend. In conclusion, dietary supplementation with marine red yeast significantly increased the growth performance, antioxidant capacity, initial immunity, lipid synthesis, and mTOR signaling pathway in juvenile GIFT tilapia. Based on the second-order polynomial regression analysis, the optimal dietary marine red yeast level was between 0.53 % and 0.60 %.