Digestive enzymes of the anchovy Engraulis capensis in relation to diet

Abstract

The anchovy Engraulis capensis (Glch.) is capable of exploiting both diatoms and Crustacea as a food resource. Much of the crustacean exoskeletal matenal passes into the hindgut after initial disruption in the stomach. Both laminarinase and α-amylase activity are relatively low in the oesophagus and stomach, but increase in the caeca and lumen of the intestine. There is no evidence of cellulolytic activity in the gut although numerous gut bacteria occur in the caeca and lumen of the intestine. Distribution of protease activity in the gut follows that of carbohydrases, most proteolytic activity being present in the lumen of the intestine, rather than in the oesophagus or stomach. In contrast, chitinase activity is found early in the digestive pathway and is capable of attacking the chitinous exoskeleton of Crustacea in the stomach, prior to hydrolysis of their contents by carbohydrases and proteases. Bacteria isolated from the intestinal caeca do not hydrolyse chitin, nor do they degrade long-chain polysaccharides or azocasein. Most of the isolates were capable of utilisation of simple sugars commonly found in diatoms and released following hydrolysis of polysaccharides, and also of utilisation of N-acetylglucosamine formed as an endproduct of chitin hydrolysis. Anaerobic strains were, in addition, capable of urea utilisation. Our data thus suggest that digestive enzymes allow E. capensis to exploit a wide range of food items, including diatoms and Crustacea, without bacterial involvement. The gut microflora may be primarily maintained by uptake of the endproducts of carbohydrate, protein and chitin degradation.