Effects of dietary lentinan on growth performance, nonspecific immunity and disease resistance to Aeromonas hydrophila in largemouth bass (Micropterus salmoides)

A study was conducted to evaluate the effects of dietary lentinan (LNT) on growth performance, nonspecific immunity and disease resistance to Aeromonas hydrophila in largemouth bass (Micropterus salmoides). Largemouth bass (initial weight: 10.31 +/- 0.25 g) were divided into the CK, L1, L2, L3, L4 and L5 groups in triplicate and fed with diets containing LNT at 0%, 0.05%, 0.1%, 0.2%, 0.3% and 0.4% for eight weeks. Results showed that FBW, WGR, SGR and FE were significantly increased in the L3, L4 and L5 groups compared to the CK group. VSI, HSI, crude protein, crude fat and crude ash were similar among different treatment groups. Trypsin and lipase activities of intestinal tract were elevated in the L4 and L5 groups. The length of intestinal microvilli was increased in all experimental groups (P < 0.05). Lysozyme activity in serum and liver were elevated in the L3, L4 and L5 groups, SOD activity in serum and liver were elevated in the L1, L2, L3 and L4 groups, and CAT activity in serum and liver were elevated in the L4 group. Compared with the CK group, cytokine gene expressions of tnf-a and il1 beta in foregut of the L3, L4 and L5 groups were significantly down-regulated (P < 0.05), and the expression of il10 in the above three groups was significantly up-regulated (P < 0.05). After the Aeromonas hydrophila challenge test, survival rates were higher than 80% in the L4 group and lower than 40% in the CK group. In summary, our study suggested that LNT had a favorable effect on the overall health and growth of largemouth bass, and the optimal dietary concentration was 0.3%.