Supplemental effect of dietary nucleotides on hematological profile, hepatic biomarkers, antioxidant capacity, and digestive functions in Sterlet sturgeon, Acipenser ruthenus

This study investigated the effects of dietary nucleotides (NTs) on hematological indices, hepatic biomarkers, antioxidant capacity, digestive functions, and intestinal histomorphology of Sterlet sturgeon (Acipenser ruthenus). Over 10 weeks, five diets with varying levels of NTs (0 g/kg, 1.5 g/kg, 2.5 g/kg, 3.5 g/kg, and 5.0 g/kg) were fed to triplicate groups of the fish (initial weight: 95.33 ± 1.23 g) in a flow-through system. The results indicated that final weight and relative growth rate reached the highest values in fish fed with the 5.0 g/kg NTs supplemented diet (p < 0.05). The fish fed NTs-supplemented diets also had lower feed conversion ratios than those fed the basal diet (p < 0.05). While total leukocytes were increased by increasing the dietary NTs supplementation to the highest value in the fish fed with 3.5 g/kg NTs, no significant differences were obtained in RBC, Hb, MCHC, HCT, and eosinophil values among the experimental groups (p > 0.05). The highest WBC count was seen in the fish fed with 3.5 g/kg NTs compared to the control group (p < 0.05). The serum hepatic enzyme levels generally decreased with higher NTs supplementation, although alanine transaminase significantly increased at the 5.0 g/kg level (p < 0.05). The antioxidant capacity was improved in the fish fed with NTs at 0.25 and 0.35 g/kg (p < 0.05), while the serum malondialdehyde level was decreased up to 3.5 g/kg NTs but it was increased at 5.0 g/kg (p < 0.05). The protease and amylase activities peaked in the fish receiving 3.5 g/kg NTs (p < 0.05), with the highest lipase activity obtained in 2.5 g/kg NTs (p < 0.05). The intestinal histology revealed that the fish fed with NTs at 3.5 g/kg exhibited the greatest villus height and width, along with more goblet cells (p < 0.05). Based on the second-order polynomial regression analysis, the optimum dietary levels of NTs for positive effects on physiometabolic responses and intestine functions of the Sterlet sturgeon lies in the range of 2.2-3.6 g/kg.