Abstract
Studies on the digestive secretions in aquatic animals can elucidate certain aspects of their nutritive physiology. The aim of the present study was to compare the digestive lipase and phospholipase activities in ten marine species belonging to four classes following the taxonomic classification of marine organisms. All aquatic digestive tissues tested are equipped with lipase and phospholipase activities, assuming the hydrolysis of fat-rich food. The lipolytic activities determined in the pancreases of cartilaginous fishes were greater than those in bony fishes, molluscs and crustaceans. This finding might be explained by the strong digestive utilization of fat-rich macronutrients by these carnivorous fishes. A trend of activities and stabilities at different pH and temperatures for crude lipases and phospholipases from these aquatic animals suggests that the optimum pH and temperature for marine lipases are species dependent. Interestingly, the sardine caecal lipase and phospholipase were found to be mostly stable in a broad range of acidic pH values. The maximum activities of lipolytic enzymes from the hepatopancreases of Hexaplex trunculus (molluscs) and Carcinus mediterranus (crustaceans) were found to be 50 and 60 A degrees C, respectively, whereas the optimal temperature of lipolytic enzymes for the other species was classically around 40 A degrees C. Thermoactivity of molluscs' lipolytic preparations makes them potential candidates in industrial applications. Among digestive glands studied, only pancreas (cartilaginous fish) contained the classically known colipase. Regarded as the most primitive living jawed vertebrates, cartilaginous fishes represented by sharks and rays could be considered as the oldest vertebrates possessing a complex digestive system like that of mammals.