Assessment of the effect of plant inhibitors on digestive proteases of nile tilapia using in vitro assays

This study was conducted to evaluate the effect that feeding on differently treated soybean meals may have on digestive protease activity of the Nile tilapia (Oreochromis niloticus). Untreated full fat soybean (USB), heated f ullfat soybean (HSB), soaked fullfat soybean (SSB) and commercial defatted soybean meal (DSB) totally replaced fish meal (FM) in test diets (30% crude protein) fed to fish juveniles (mixed sexes) for 30 days. After this perio d, total activity of digestive proteases was determined in each group and t he ability of such proteases to hydrolyse the different protein sources and formulated feeds was tested in vitro. Significant differences were observe d between treatments, with lower values obtained for fish fed on USB, sugge sting a modification in the composition of secreted proteases. In addition, an inhibitory effect produced by wheat bran included in the test diets on protease activity of fish was also shown. The usefulness of using in vitro assays for a preliminary assessment of the nutritive value of aquafeed ingr edients is discussed.