Effect of feeding on the function and structure of the digestive system in juvenile southern catfish (Silurus meridionalis Chen)

Postprandial physiological and morphological responses to feeding were examined in juvenile southern catfish (Silurus meridionalis Chen) that had consumed a loach (Misgurnus anguillicaudatus Cantor) meal equivalent to 6?% of the body mass of the catfish. The gastric evacuation rate (GER) peaked at 4?h postfeeding, averaging 0.36?g food weight?h(-1), at which time 14?% of the ingested meal had passed into the intestine. Less than 10?% of the ingested meal remained in the stomach at 24?h postfeeding. Pepsin activity peaked at 8?h postfeeding, reaching a level approximately twofold higher than the prefeeding level. Pancreatic trypsin activity peaked at 16?h postfeeding, reaching a level 4.5-fold higher than the prefeeding level. Peaks in lipase activity in both the proximal and middle intestinal segments occurred at 16?h, reaching 2.8- and 2.4-fold higher levels than the prefeeding level, respectively, while the activity in the distal intestine segment reached a level 2.9-fold higher than the prefeeding level at 24?h postfeeding. With respect to amylase activity, only the middle intestinal segment exhibited a change, first an increase and then a decrease, after feeding. Feeding also triggered an approximately 200?% increase in the metabolic rate and resulted in 44.6?kJ?kg(-1) being expended on specific dynamic action, equivalent to 16.1?% of the meal's energy. In terms of organ size, the wet mass of the liver increased by 11?% at 24?h postfeeding, whereas the wet mass of the pancreas did not change. Except for a decrease in the thickness of the submucosa in the middle intestinal segment, the thickness of the intestinal fold, mucosa, submucosa, muscularis and serosa of each intestinal segment did not change significantly with feeding. These results suggest that the continuum of physiological responses observed with respect to metabolic increases, GER, regulation of pancreatic and intestinal digestive enzyme activities and liver wet mass to feeding corresponds to the changes in the demand on the digestive system in S. meridionalis. Moreover, species maintained stable gastrointestinal tract morphology during the short interval of repeated feeding.