Enzyme activities and pH variations in the digestive tract of gilthead sea bream

Two investigations were carried out with 150 g gilthead sea bream Sparus aurata to determine the relative activity of six digestive enzymes (pepsin, trypsin, chymotrypsin, carboxypeptidase A. carboxypeptidase B and amylase) and the pH variation in the lumen of different parts of the gut of fish fed one or two meals per day. Pepsin activity was found exclusively in the stomach. whereas activities of the other enzymes studied were found in all regions of the out, including the stomach. The lack of localization of enzyme production in the digestive tract of S. aurata is similar to many other species as reported in the literature. The pH variations found in the different regions of the gut could be explained by general digestive physiology following the flow of digesta along the digestive tract. The range of pHs recorded in the various regions of the gut were generally outside the cited optima for many digestive proteases in this species. (C) 2003 The Fisheries Society of the British Isles.