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The proteolytic activities of the digestive tract of three carnivorous fish species (Sebastes mentella, Scophthalmus maximus, Sparus aurata) have been studied. The activity found in the stomach showed a pH optimum of 2.0 for all species, whereas this was in the alkaline range (9.5-10.0) in the intestinal extracts. Similar optimal temperature was measured for all species, although higher residual activities were detected at low temperatures in redfish and turbot. Lower E a values were detected in stomach than in intestine. The effect of HCl concentration on protein digestion differed between stomach and intestine being inhibitory in the former. The main proteolytic enzyme for the acid activity of the stomach of the three species seemed to be a pepsin. However, the enzymatic composition of the intestine was more species specific.

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The amylase activity of the digestive tract of three carnivorous fish species (Sparus aurata, Scophtalmus maximus and Sebastes mentella) has been studied. The activity of seabream and turbot showed its maximum at neutral pH (7.0-7.5); meanwhile, the activity of redfish had an optimum pH at 4.5-5.0. The tº function ranged between 35 and 45°C for the three species. The Arrhenius plots of the intestinal activities of seabream and turbot showed breakpoints at temperatures close to those of their physiological activities. High saline concentrations inhibited the activity of seabream and turbot and activated the activity of redfish. Seabream activity was absolutely dependent on calcium ions. On the contrary, redfish activity was only detected in the absence of this metal. Studies carried out by using several effecters suggested that the activities found in these three species are different. Considering our results from a point of view of the environmental conditions of these species, it might be concluded that enzymatic digestion of dietary carbohydrates proceeds at very low rate. Physiological implications are discussed.

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