Dietary nucleotide administration influences growth, immune responses and oxidative stress resistance of juvenile red sea bream (Pagrus major)

• No previous work has addressed the effect of mixed nucleotide for Pagrus major.
• Therefore, effects of a mixture of IMP, AMP, GMP, UMP and CMP at 0, 0.5, 1.0, 1.5, 2.0 and 2.5 g kg− 1 were studied.
• Fish performances were significantly improved by dietary nucleotide administration.
• Supplementation of mixed nucleotides enhanced immune response and antioxidant status of Pagrus major.
• The optimum supplement of dietary mixed nucleotide for Pagrus major is 1.0–1.5 g kg− 1.

A 56- day feeding trial was carried out to determine effects of purified nucleotide mixture for red sea bream (Pagrus major). Five dietary level of purified nucleotide mixture containing equal portion of inosine 5′ monophosphate (IMP), adenosine 5′ monophosphate (AMP), guanosine 5′ monophosphate (GMP), uridine 5′ monophosphate (UMP) and cytidine 5′ monophosphate (CMP) were supplemented to the basal diet (control, D1) at 0.5 (D2), 1.0 (D3), 1.5 (D4), 2.0 (D5) and 2.5 (D6) g kg− 1. Triplicate groups of fish (initial weight: 2.6 g) were stocked in 100-L polycarbonate circular tanks at a density of 18 fish per tank under the flow-through system, and were fed the respective test diets twice daily to satiation level. After feeding trial, significantly higher growth performances, survival (%) and feed utilization were observed in fish fed with 1.5% mixed nucleotide supplemented diet (D4). Growth performance parameters were not differed significantly among diet groups D3 and D4. Feed conversion ratio, protein efficiency ratio and survival were not differed among diets D2 to D5. All the growth and feed utilization parameters were significantly lower in D1 and D6. In case of oxidative stress parameters fish fed nucleotide supplemented diets showed best condition because of the least oxidative stressed condition as well as the highest tolerance against oxidation. Stress resistance against low salinity exposure (LT50), significantly increased with nucleotide supplementation and was highest in D4. Total serum protein, serum lysozyme activity and total peroxidase content tended to be higher (P > 0.05) in nucleotide supplemented group. Catalase activity reduced (P < 0.05) with nucleotide supplementation and significantly lower value obtained in D3 and D4 diet groups. Bactericidal activity was also increased (P < 0.05) with the supplementation of nucleotide in diets regardless of the inclusion levels. Considering overall performance of fish in a 56 days growth trial, it is therefore recommended a dietary administration of 1.0–1.5 g kg− 1 mixed nucleotides to promote growth, immune responses and stress resistance of juvenile red sea bream.