Developmental changes of digestive enzymes in Persian sturgeon (Acipenser persicus) during larval ontogeny

The development of digestive enzymes from the stomach (pepsin), pancreas (trypsin, chymotrypsin, α-amylase and lipase) and intestine (alkaline phosphatase) was studied in Persian sturgeon (Acipenser persicus) from hatching to the juvenile stage at 40days post hatching (dph). Larvae were obtained from artificial propagation of one male and one female and transferred to larval culture tanks where, after yolk sac absorption (9dph at 17–18°C), they were fed with Artemia urmiana and Daphnia sp. The assessment of the activity of digestive enzymes showed that at the onset of exogenous feeding, gastric glands were already functional as indicated by the increase in pepsin specific activity. In contrast, alkaline proteases like trypsin and chymotrypsin decreased their specific activity after the onset of exogenous feeding, indicating the importance of these types of enzymes in the cleavage of yolk proteins during the endogenous feeding phase and the replacement of the larval alkaline-type digestion by a juvenile-type acid digestion. After the first feeding, amylase and lipase specific activities increased. Such increments in the activity of amylase might be genetically programmed to better digest carbohydrates in diets with the goal of sparing proteins during the larval stage, whereas the increase in lipase was related to changes in the lipid content of live prey and the progressive maturation of the pancreatic function during larval development. Changes in enzyme activities from the stomach and pancreas were coupled with that in the intestine (brush border membrane), where the specific activity of alkaline phosphatase progressively increased until 19–24dph and remained constant thereafter, indicated the maturation of the intestine and the achievement of a juvenile-like mode of digestion. Considering these data on the digestive enzymes from the pancreas, stomach and intestine, Persian sturgeon larvae might be weaned around 19–24dph, as larvae have achieved the complete maturation of their digestive functions by this date. This developmental process, and particularly for the digestive functions, can be considered as a reference to evaluate the effect of a formulated micro diets feeding on larvae.