Effect of diets containing a purified soybean trypsin inhibitor on growth performance, digestive proteases and intestinal histology in juvenile sea bream (Sparus aurata L.)

Abstract

Juvenile sea bream were fed on diets containing 0.0, 2.0 or 4.0 g/kg of a soybean trypsin inhibitor (SBTI) for 30 days. The growth performance, total protease activity and intestinal histology were studied after 0,15 and 30 days of dietary treatment. No signi¢cant di¡erences were found in the weight gain, speci¢c growth rate (SGR) and feed conversion rate in fish fed on inhibitor-supplemented diets when compared with those fed on an inhibitor-free diet. Only the SGR at day 15 decreased signi¢cantly with protease inhibitor inclusion, although this effect was not observed at day 30. In relation to proteolytic activity at day 15, the total protease activity in the distal intestine decreased in ¢sh fed on inhibitor-supplemented diets. Zymograms of these extracts showed that the SBTI reduced the intensity of some proteolytic fractions in the distal intestine. A noticeable reduction in the protease activity of the intestinal content in fish fed onthe highest level of soybean inhibitor (4.0 g/kg) was also observed. However, at day 30, the inhibition e¡ect on these active bands was not detected, and the total protease activity was similar to that in ¢sh fed on an inhibitor-free diet. Histological examination revealed no perceptible differences in the intestinal structure between any of the diet groups. In addition, all ¢shweremaintained under experimentation for 10 more days and fed on an inhibitor-free diet to determine whether the possible effects caused by the protease inhibitor could be reverted.The administration of SBTI-supplemented diets did not affect sea bream growth performance or intestine histology after 30 days, and only a decrease in the total alkaline protease activity was found at day 15.