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

- Dietary supplementation of IMP on muscle growth and growth-related gene expression were evaluated in Nile tilapia.
- Final body weight of Nile tilapia was higher in 0.2 to 0.8% IMP supplemented diet.
- IMP supplementation (0.2-0.4%) enhanced the growth of tilapia by promoting muscle fiber hyperplasia and hypertrophy.
- Growth-related gene expression was also upregulated in 0.2 to 0.8% IMP supplemented diet.
- Supplementation of ≥ 0.2% IMP is the most effective for enhancing growth of Nile Tilapia.

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 ± 0.1 g) were stocked in 15 fiberglass tanks (150 L 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 60 days. 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 = ≤ 10 μm) and hypertrophic (diameter class 60 = 50 > d ≤ 60 μm and class 70 = d > 60 μm) 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.Statement of relevance-In most cases, fish growth was analyzed by calculating the increase in size or weight of fish. However, fish/muscle growth are controlled by different cellular and molecular pathways, which are poorly studied areas in aquaculture and nutritional studies. A research was conducted to investigate the effects of dietary supplementation of inosine monophosphate on: (1) cellular muscle growth characteristics, and (2) expression of major growth-related genes (GH, GHR-1, IGFs, MRFs, Pax7 and myostatin) in juvenile Nile tilapia. This research will help to understand the reason behind the improved growth or production of fish with a specific nutrient or diet.