Effects of dietary n-3/n-6 polyunsaturated fatty acids ratio on growth performance and growth-related genes mRNA expression in common carp (Cyprinus carpio haematopterus)

To analyze the influence of n-3/n-6 PUFAs levels on the growth performance and growth- related genes mRNA expression in common carp, five isonitrogenous and isoenergetic experimental diets based on fish oil and mixed vegetable oil were fed to the Cyprinus carpio haematopterus for 10 weeks. The control diet (T1) was only supplemented with fish oil as lipid source, n-3/n-6 ratio was 0.97. the second group (T2) was only supplemented with peanut oil, n-3/n-6 ratio was 0.02. n-3/n-6 ratio of the other three experiments groups were 0.46(T3), 1.09 (T4) and 1.53 (T5) with peanut oil and perilla seed oil as feed source. After 10 weeks cultivation experiments, we checked each group for fish growth performance, serum growth hormone and growth-related gene expression level in different parts of muscle tissue. The results indicated that there were no significant differences in the viscerosomatic index (VSI), feed coefficient (FCR), feed intake(FI)among the five tested groups. Weight gain rate of the fish (WGR) was raised first and subsequently declined with the increase of the n-3/n-6 ratio. WGR climbed the peak at T4 group. The serum GH levels of T2 group were significantly higher than those of others, and the level of GH in serum gradually reduced with the increase of of n-3/n-6 ratio. The expression levels of growth-related genes in the dorsal muscles showed that gh, ghr, igf-1 and myodwere enhanced first and subsequently declined. However, igf-1rdisplayed the opposite expressive trend, while there were no significant differences in mstn level among the five treated groups. In red muscle, the expression levels of gh and myod were gradually decreased with the increase of n-3/n-6 ratio, and the expressions of ghr and mstnexhibited no significant differences in five groups. Besides, the expressive trends ofigf-1 and igf-1r were similar to that of dorsal muscles. Interestingly, the expressions of gh, ghrand igf-1 in the abdominal muscles were consistent with the dorsal muscles. But, the levels of igf-1r and myod manifested no significant difference in five tested groups. There were significant differences in the number of muscle fibers in the T2 group and T4 group, and the muscle fibers in T4 group were thicker than those of T2. This study showed that vegetable oil contributed to improve the WGR of the fish and the n-3/n-6 ratio of the diets not only affected the serum GH level, but also influenced the growth related genes of GH/IGF axis in different parts of the muscle tissues.