Distribution of intestinal enzyme activities along the intestinal tract of cultured Nile tilapia, Oreochromis niloticus L.

Abstract

Regional distribution of intestinal enzymes in Nile tilapia was investigated using enzyme histochemistry. Samples from adult fish were obtained from the five major intestinal segments. Activities of maltase, leucine aminopeptidase, dipeptidyl aminopeptidase IV, lipase, non-specific esterases, and alkaline phosphatase were examined in each segment. All enzymes were present at specific sites along the first four intestinal segments. Strong reaction for maltase was present in the third intestinal segment, while aminopeptidases and alkaline phosphatase were detected in the first three parts. The most intense activity for lipase was present in the first two parts, while non-specific esterases were observed in the first four portions. Activities of all these enzymes were demonstrated in the brush border. Non-specific esterases were also present in the cytoplasm of the enterocytes. In addition to its brush border localization in the cranial segments, dipeptidyl aminopeptidase IV was also observed in the basal lamina of all segments, including the terminal segment. These results suggest that the first four regions play the most important role in both digestion and absorption of nutrients. In addition, the great length of the portions of the intestinal tract participating in digestion provides abundant surface area for nutrient absorption, and is likely one factor involved in the rapid growth rate characteristic of tilapian fish.