Effects of dietary umami taste stimulator on appetite, growth, antioxidant capacity, intestinal histology and target of rapamycin pathway related genes’ expression in largemouth bass (Micropterus salmoides) fed a high plant protein diet

The present study investigated the potential effects of an umami taste stimulator (UTS) on largemouth bass ( Micropterus salmoides ) fed a high plant protein diet. Two isonitrogenous and isolipidic diets were formulated with 40% fishmeal (positive control, PC) and 25% fishmeal (negative control, NC), respectively. The other three diets were supplemented with 0.10%, 0.15% and 0.20% of the UTS based on NC group. Five groups of fish (mean initial weight 29.82 ± 0.04 g) were fed twice daily for 64 days. The results indicated that feed intake, growth performance, and taste receptor and enteroendocrine-related genes expression ( pyya, t1r1 and ghrl ) in NC group were significantly reduced compared with PC group, which were improved with dietary supplementation of the UTS (at 0.15% and 0.20%). In addition, muscle thickness of midgut and hindgut, villus length of hindgut in the NC group were reduced compared to the PC group, but they improved with dietary UTS supplementation. Also, antioxidant capacity, and expression of genes involved in peptide and amino acid transport and target of rapamycin (TOR) pathway were reduced in the NC group compared to the PC group. However, the inclusion of UTS improved the total antioxidant capacity, superoxide dismutase and catalase compared with the NC group. Peptide and amino acid transporters ( lat1 , lat2 , snat2 and pept2 ) and TOR pathway ( tor , akt1 , 4ebp1 and s6 ) related genes’ expression were also ameliorated by UTS addition compared to the NC group. In summary, UTS supplementation could improve the appetite, growth performance, and health status of largemouth bass, and the recommended additional amount of UTS was 0.15%–0.20%.