Partial Substitution of Fishmeal by Meat and Bone Meal, Soybean Meal, and Squid Concentrate in Feeds for the Prawn, Artemesia longinaris: Effect on Digestive Proteinases

The effect of alternative protein sources on proteinase activity in the midgut gland of Artemesia longinaris was studied. Three isoproteic feeds were compared: a basal diet containing 48% fishmeal and 17% soybean meal (diet 1), the basal diet containing meat and bone meal as partial replacement of the fishmeal (diet 2), the basal diet containing additional soybean meal and a squid protein concentrate as partial replacement of the fishmeal (diet 3). Midgut gland extracts from the three treatments and wild prawns (control) were assayed to quantify proteinase activity. Specific inhibitors were used to identify proteinase classes by SDS-PAGE. Specific proteolytic activity was highest in the wild prawns and in prawns fed diet 2. Trypsin activity was higher in prawns fed the diets (1.9-2.6 absorbance/min/mg) than in wild prawns (0.6 absorbance/min/mg). Chymotrypsin activity was highest in prawns fed diet 2. Proteinase activity in samples on azocasein was inhibited by soybean trypsin inhibitor and N alpha-p-tosyl-L-lysine chloromethyl ketone. Electrophoresis revealed at least six different bands with zones having caseinolytic activity in prawns fed the diets as compared to wild prawns, including four trypsins (16.6, 18.2, 21.9, and 25.1 kDa) and one chymotrypsin (53.7 kDa). Our findings indicate that proteolytic activity in A. longinaris adapts to the quality of the dietary protein and that fishmeal can partially be replaced by additional soybean meal in combination with squid protein concentrate.