Ontogeny of digestive tract of Stellate sturgeon (Acipenser stellatus) from hatching to juvenile stage: Digestive enzymes activity, stomach and proximal intestine

Abstract This study was an attempt to evaluate ontogenic development of digestive enzymes activity, histomorphological changes of stomach and proximal intestine of Stellate sturgeon (Acipenser stellatus) from hatching up to 50 days post hatching (dph). The digestive enzymes activity of pepsin, trypsin, chymotrypsin, alkaline phosphatase, amylase and lipase was considered. Pepsin activity was detected in one-day-old prelarvae followed by a sharp increase at the beginning of larval stage (i.e., 8 dph) onward. However, few fluctuations coincided with changes of food types consumed by the fish. The highest chymotrypsin activity was observed at 1 dph. During larvae period, the enzyme activity showed two surges that occurred at 15 and 31 dph. Although descending trends for trypsin (with the highest activity at 8 dph) and amylase (with the highest activity at 24 dph) were observed, lipase and alkaline phosphatase revealed an incremental trend during early growth stages. At 10 dph, functional stomach was observed with epithelia containing some crypts. Intestinal morphometric indices such as intestinal folds were measurable at 4 dph; epithelium, however, appeared immediately after hatching. Pearson's correlation coefficient revealed positively related activities of trypsin, chymotrypsin and amylase. They all reflected negative relationships with pepsin, alkaline phosphatase and lipase. The findings suggest that gastric digestion of proteins become dominant during the ontogenetic development of Stellate digestive tract. Over this period, the fish relied on energy dense lipid molecules to meet their metabolic demands while they spare protein for further tissue synthesis/maintenance. Moreover, pepsin seems to be more responsive to the type of food consumed by the Stellate and might be a useful indicative of the nutritional status assessment of the fish. The concluding remarks are discussed in light of the significance of various histological changes and their interrelations with ontogeny of digestive enzymes activity.