Ontogeny of the digestive enzyme activities in hatchery produced Beluga (Huso huso)

• Beluga larvae had a developed intestine at the onset of exogenous feeding.
• More Beluga weaned earlier, more larvae will live.
• Weaning should begin immediately after commencement of exogenous feeding.
• Complete substitution of live prey by inert feed is not recommended until 235 ddph.

The development of digestive enzymes of the stomach (pepsin), pancreas (trypsin, chymotrypsin, amylase, and lipase) and intestine (alkaline phosphatase) were studied in Great sturgeon or Beluga (Huso huso) from hatching time to 50th day post hatching. Sampling was carried out immediately after hatching, 111.3, 235.2, 306, 400.2, 490, 612.5, 756 and 906.5 degree days post hatching, ddph (0, 7, 14, 18, 23, 28, 35, 42 and 50 days post hatching, dph, respectively). Beluga larvae had near 70% mortality during rearing procedure. The highest mortality rate was accrued in two stages; firstly, during endogenous feeding (2–9 dph; 30.4–144.9 ddph) and then from a mixed feeding stage (12 dph; 253.5 ddph) until the starting time of weaning (28 dph; 490 ddph), with values ranging from 50 to 40% of total mortality, respectively. Furthermore, the results showed that at the onset of exogenous feeding, gastric glands were already functional as indicated by the steady increase in pepsin specific activity. In contrast, trypsin and chymotrypsin significantly decreased after the onset of exogenous feeding, showing the importance of these types of enzymes in the cleavage of yolk proteins during the endogenous feeding phase. Moreover, amylolytic activity fluctuated considerably over the study period; after onset of exogenous feeding alpha-amylase activity increased (P < 0.05), whereas it reached a maximum value at the end of the study (P < 0.05). Lipolytic activity was low in the first week (P < 0.05), whereas it increased until the onset of exogenous feeding and then, until 490 ddph (28 dph) went down again and reached the same amount in the first week. At the end of the study, lipolytic activity reached 4 times more relative to the activity levels recorded during the first 4 weeks of exogenous feeding. Furthermore, changes in enzyme activities from the stomach and pancreas were coupled with those in the intestine (brush border membrane), whereas the increase in alkaline phosphatase from hatching until 111.3 ddph (7 dph) and reaching a maximum value between 111.3 ddph and onset of exogenous feeding at 235.2 ddph (14 dph), suggested that the Beluga larvae had a developed intestine at the onset of exogenous feeding. The results obtained from this study proposed that, more Beluga weaned earlier, more larvae will live and hence weaning should begin immediately after commencement of exogenous feeding.