Dietary supplementation of inosine monophosphate promotes cellular growth of muscle and upregulates growth-related gene expression in Nile tilapia Oreochromis niloticus

Muscle growth mechanisms are controlled by different cellular and molecular pathways, and dietary supplementation of nucleotides (NTs) may play an important role to influence such pathways in fish. In this study, we hypothesized that dietary supplementation of inosine monophosphate (IMP) would enhance cellular muscle growth, and upregulate growth-related gene expression in juvenile Nile tilapia Oreochromis niloticus. Five isonitrogenous (40% crude protein) and isocaloric (20.3 KJ/g diet) test diets were formulated by supplementing 0, 0.1, 0.2, 0.4 and 0.8% IMP in casein and fishmeal based semi-purified diet. Triplicate groups of juvenile Nile tilapia (0.59±0.1g) were stocked in 15 fiberglass tanks (150L capacity), arranged in a simple biological filters-based closed system, with stocking density of 25 individuals per tank. The feed was applied at a daily feeding rate of 10% body weight (BW) initially and reduced to 5% BW finally for 60days. Treatments results were compared using ANOVA (α=0.05). At 60th day (60 D), final body weight of fish fed with 0.2–0.8% IMP were significantly higher than that of fish fed without IMP supplemented diet. At 60 D, both the hyperplastic (diameter class 10=≤10μm) and hypertrophic (diameter class 60=50>d≤60μm and class 70=d>60μm) muscle fiber frequency were significantly higher in 0.2–0.8% IMP supplemented diets compared to 0–0.1% IMP supplemented diet. Two-way ANOVA result demonstrated that the pituitary GH, hepatic IGF-1 and GHR-1, and muscle-specific MyoD, myogenin and Pax7 gene expression were upregulated in fish fed with 0.2–0.8% IMP compared to the fish fed without IMP supplemented diet. However, hepatic IGF-2 and myostatin gene expression were not significantly affected by the dietary treatments. Real-time PCR data also demonstrated that myostatin gene expression was downregulated and all other gene expression were upregulated at the end of feeding trial (60 D) compared to the initial period (1 D). The results of the present study indicated that IMP supplementation enhanced the muscle growth by promoting hyperplasia and hypertrophy, and upregulating the growth-related gene expression in Nile tilapia. In conclusion, IMP is a potential feed additive and supplementation of ≥0.2% IMP is the most effective for enhancing growth of Nile Tilapia.