Dietary functional palatability enhancer improved growth and appetite in largemouth bass (Micropterus salmoides) fed a reduced fish meal diet

This study aimed to investigate the feasibility of using a functional palatability enhancer (PE) to promote healthy growth of largemouth bass ( Micropterus salmoides ). A positive control diet (PC) was formulated in which fish meal content was 45 %, and in the negative control diet (NC) fish meal was reduced to 27 % and substituted with soybean protein concentrate. A third experimental group consisted of the NC diet supplemented with 0.15 % PE (NC + PE). The 360 juvenile M . salmoides (13.44 ± 0.03 g) were cultured for 8 weeks in 12 recirculating tanks, 4 per experimental group. Results indicated that fish fed the NC diet exhibited lower growth and feeding efficiency (PWG, SGR, FE and PER) than those fed the other diets. Moreover, both HSI and VSI substantially decreased in the NC and NC + PE groups compared to the PC group. The highest mid-hindgut activities of trypsin and pepsin were exhibited in fish fed the NC + PE diet, which presented the lowest T-CHO and LDL-C levels in serum and liver. Fish fed the PC diet had higher activities of GOT and GPT in serum, but the lowest GSH and T-AOC activities in serum and mid-hindgut. The activity of CAT was significantly up-regulated in serum and mid-hindgut of fish fed the NC + PE diet, along with the expression of genes akp and il-10 in the mid-hindgut, while the expression of tlr2 and myd88a was the lowest. Gene expression of anorexigenic factors ( pomc and cart ) in hypothalamus was substantially down-regulated in fish fed with NC + PE. The lowest level of ins in mid-hindgut and stomach was detected at fish fed the NC + PE diet. Overall, the study demonstrated that the tested PE enabled reducing fish meal level without negatively impacting growth, feed utilization, appetite and health parameters of M . salmoides . • Adding 0.15 % palatability enhancer to largemouth bass diet improved growth due to 18 % reduction in fishmeal. • Dietary 0.15 % palatability enhancer supplementation reduced lipid deposition in serum and liver and promoted liver health. • Dietary 0.15 % palatability enhancer supplementation enhanced immunity and antioxidant activity. • Dietary 0.15 % palatability enhancer supplementation markedly alleviated anorexigenic factors.