Dietary effect of actinidin enzyme on growth, digestive enzymes activity, immunity, liver and intestine histology of juvenile sterlet sturgeon (Acipenser ruthenus)

This 56-day experiment examined the effect of actinidin added to commercial feed at concentrations of 0 g (control group C), 10 g (A1 group) and 20 g (A2 group) kg−1diet on growth, feed utilization, intestinal morphology, digestive enzyme and immune response of juvenile sterlet (Acipenser ruthenus). A total of 270 juvenile sterlet with an average body weight of (46.21 ± 0.37 g) were divided into nine tanks (280 L for each), with 30 fish per tank (three replicates each) under a recirculating aquaculture system (RAS). At the end of the experiment, distinct differences in the mean body weights of the fish were observed, with the greatest differences (P < 0.05) noted in A1 group (112.88 ± 1.20 g). The mean body weight in group A2 (106.40 ± 1.37 g) was statistically significantly (P < 0.05) higher compared with control group C (87.80 ± 1.51 g). A significant decrease in the activity of alkaline phosphatase (ALP) was noted in the liver in A2 group (57.72 IU g−1) compared with the control group (127.38 IU g−1). In the hindgut part of the intestine, a significant increase in the activity of alkaline phosphatase (ALP) was noted in A2 group (179.06 IU g−1) compared with the control group (92.44 IU g−1). An analysis of the immunity response showed an increase in the lysozyme value in A1 and A2 groups. In these groups, the immunoglobulin (Ig) content increased statistically significantly compared with the control group. A significant increase was noted in the phagocytic killing activity in the pronephros of fish fed feed supplemented with actinidin. A higher metabolic activity of macrophages and a higher phagocytic killing activity were also noted in the spleen in A1 and A2 groups. Based on the experiment, it can be concluded that the actinidin has a positive effect on Sterlet growth and stimulates its immune system.