The Effects of Dietary Nucleotide and P. acidilactici on Growth Parameters, Serum Biochemical and Immunity Parameters, and Disease Resistance of Rainbow Trout (Oncorhynchus mykiss) Against Aeromonas hydrophila

This study was conducted to investigate the effects of dietary nucleotide and P. acidilactici on the growth performance, some innate immune responses and serum biochemical parameters as well as the resistance of rainbow trout (Oncorhynchus mykiss) against Aeromonas hydrophila. Nine experimental diets were formulated to contain three dietary nucleotide levels (0, 1 and 3 g kg-1 diet) and three P. acidilactici levels (0, 0.1 and 0.3 g kg-1 diet) according to a 3×3 factorial design. Each diet was randomly assigned to triplicate groups of 30 fishes (with the average initial weight of 63.4±1.62 g) per tank. At the end of an eight week feeding trial, several innate immune responses and serum biochemical parameters including serum total protein, lysozyme, serum alternative complement (ACH50), cholesterol, triglycerides, albumin, and glucose levels and also fish performance (survival, weight gain, specific growth rate (SGR) and feed conversion ratio (FCR)) were measured. The results indicated that lysozyme and ACH50, were all increased significantly (P0.05). The results also showed that the interaction between dietary nucleotide and P. acidilactici significantly improved fish performance in the rainbow trout. Furthermore, at the end of the feeding trial, ten fish per each replicate were intraperitoneally injected with A. hydrophila to determine the disease resistance. The results showed that the supplementation of the rainbow trout diet with dietary nucleotide and P. acidilactici remarkably increased resistance to A. hydrophila infection; the highest resistance was also observed in the interaction groups (dietary nucleotide × P. acidilactici). Overall, the combination of dietary nucleotide and P. acidilactici showed more advantages than the administration of individual ones. The best combination of them for the rainbow trout was 3 g kg-1 dietary nucleotide and 0.1 g kg-1 P. acidilactici.