Substitution of dietary fishmeal by soybean meal with inosine administration influences growth, digestibility, immunity, stress resistance and gut morphology of juvenile amberjack Seriola dumerili

Abstract We determined the dietary inosine effects in gradually replaced fishmeal (FM) with soybean meal (SBM) protein-based diets on growth, digestibility, immunity, stress resistance and gut morphology of juvenile amberjack. Seven experimental diets were formulated to be nearly isonitrogenous (48% crude protein) where diet 1 (D1) was FM based control diet. Diet 2 to 7 were formulated by replacing 25, 50 and 75% of FM protein with SBM and each replacement level was supplemented with or without inosine at 0.6% for diet groups D2(FM25INO), D3(FM25), D4 (FM50INO), D5(FM50), D6(FM75INO) and D7(FM75), respectively. Triplicate groups of fish (24.9 g) were randomly stocked in 200 L polycarbonate tanks at a rate of 24 fish per tank and fed to satiation twice daily for 56 days. After the feeding trial, final weight, specific growth rate, and weight gain were not significantly different among the treatments with that of the 50% replacement containing inosine. Without inosine-supplemented 50% replaced group and with or without inosine-supplemented 75% replaced group showed reduced growth and feed utilization performances. The apparent digestibility coefficients of dry matter, protein and lipid were significantly higher in control and other replacement groups with inosine supplementation. In the case of oxidative stress parameters, fish fed inosine-supplemented diets showed the best condition. Stress resistance against low salinity exposure (LT 50 ), significantly increased with inosine supplementation and was highest in inosine-supplemented 50% replacement diet group. Total serum protein (TSP), alternative complement pathways (ACH 50 ), lysozyme activity (LA), bactericidal activity (BA) and peroxidase activity (PA) tended to be higher in inosine-supplemented groups compared to the non-supplemented groups. Simultaneously, enterocyte height, fold height, and microvillus height of the anterior and posterior enteric sections increased significantly with the inosine supplementation. Results of the study indicated that at least half of the fishmeal could be replaced with soybean meal and supplementation of inosine in the diets of juvenile amberjack. Moreover, inosine administration in 50 to 75% FM replacement groups could be helpful to improve the digestibility, immune responses, stress resistance, and intestinal health condition of fish.