Influence of Dietary Nucleotides on Growth Performance, HSP70 Expression, and Stress Resistance in Kutum (Rutilus kutum) Fry

BACKGROUND: Nucleotides (NT) are known as semi- or conditionally essential nutrients which might occasionally become essential in pathological and stress conditions that demand intense nucleic acid and protein synthesis.OBJECTIVES: A feeding trial was conducted to evaluate the effects of NT supplementation on growth performance and stress resistance of fry kutum (Rutilus kutum).METHODS: A basal diet was supplemented with 0 (control), 0.3, 0.5, and 0.7 g NT kg-1 to formulate four experimental diets. After eight weeks of feeding trial, the growth parameters were evaluated and then fish exposed to osmotic stress. To elucidate the underlying physiological mechanisms, cortisol and HSP70 levels were measured at selected times of 0, 2h, 8h, and 24h after the osmotic shock.RESULTS: According to the results of growth parameters after eight weeks of feeding trial, fish fed diet with 0.7 g NT kg-1 had the highest final weight and DGR compared with the other treatments (P<0.05). However, no significant differences were observed concerning FCR, SGR, CF, and PER between the treatments (P>0.05). The results of HSP70 revealed that fish fed with NT had higher levels of HSP70 expression. Additionally, the levels of HSP70 at 2h increased significantly by 3-7-folds over the baseline levels (0h), and then decreased significantly at 24h; however, HSP70 levels at 24h was 1-3-fold over the baseline levels. The findings of cortisol showed that Cortisol values were significantly affected by dietary NT levels (P<0.05) and lower stress-induced cortisol and glucose elevation were observed in all the NT groups compared to the control group. Moreover, plasma cortisol levels reached a significant peak 2h after the salinity stress. This value decreased significantly after 8h, returning to the pre-stress levels by 24h (P>0.05).CONCLUSIONS: Our data indicated that NT administration promoted growth performance and increased the ability of resistance to osmotic stress during freshwater to seawater transfer in fry kutum.