Digestive enzymes profile of the midgut gland of juvenile painted river prawn (Macrobrachium carcinus)

Abstract

This study assessed the activity of the main digestive enzymes in juveniles of the painted river prawn Macrobrachium carcinus. Prawns reared in 24 m2 tanks at a density of 10 individuals. m−2 for 45 days were fed a commercial diet with 40 % crude protein. A sample of 21 prawns with 2.92 ± 0.60 g and 27.87 ± 1.50 mm had their midgut glands (MG) dissected. Assays prospecting total proteolytic activity, total amylase, α-amylase, trypsin, chymotrypsin, β-galactosidase, agarase and lipase in the MG were performed. The activities of several aminopeptidase (alanine, arginine, glycine, histidine, isoleucine, leucine, proline and tyrosine aminopeptidase) were also evaluated. In addition, the effect of calcium (CaCl2) on trypsin activity was assessed. The following mean (± SD) activities were found: total proteolytic activity (8.00 ± 0.003 U.mg-1); total amylase (0.322 ± 0.002 U.mg-1); α-amylase (8.730 ± 0.008 U.mg-1); trypsin (12.7 ± 0.001 mU.mg-1); chymotrypsin (19.94 ± 0.0019 mU.mg-1); β-galactosidase (59.4 ± 0.18 U.mg-1); agarase (13.34 ± 0.15 U.mg-1) and lipase (0.019 ± 2.73 U.mg-1). Amongst aminopeptidases, only alanine, arginine, glycine and leucine aminopeptidase were found to be active. At concentrations from 5 to 90 mM, the activity of trypsin was not affected by CaCl2. Compared to other prawn species, M. carcinus has a wide range of digestive enzymes and a tendency towards greater use of animal protein. As studies on the digestive enzymes of juvenile prawns of the Macrobrachium genus are scarce, the present results represent basic data that may serve as a reference for future studies and also aid in the formulation of diets specific for this important group of crustaceans.