Digestive protease activities of juvenile and adult eel (Anguilla japonica) fed with floating feed

Two pepsins, designated P I and P II were isolated from the stomach of juvenile and adult eels. The optimal pH of P I was 1.5 for juvenile (50 5 g) and 2.0 for adult eel (150 +/- 10 g), while that of P II was 3.5 for both eels. P I in juvenile eel was 1.5 to 2.0 times more active than that in adult. NaCl at 0.14 to 0.21 mM activated P I activity to two times of that without the presence of salt. P II activity was not affected by salt. Trypsin at optimum pH 8.0 and chymotrypsin at optimum pH 7.0 seemed to correlate with the quantity of digesta in the organ while pepsin activity bore no correlation with digesta. The profile of post-feeding digestive proteases was different between feed in pelleted form and in paste form as a result of its susceptibility for proteases to diffuse into the feed digesta. These post-feeding observations were obtained during a 14-month feeding trial. The only difference between eels fed the float diet or the paste diet was the 24-h profile of the post-feeding digestive protease activity in the tissue and digesta of the gastrointestinal tract. It seems that the susceptibility of the ingested feed to be broken down into particles of smaller sizes, i.e., 0.1 mm diameter, for proteases to readily diffuse into the digesta was a determining factor for in vivo digestion in eel. (C) 2002 Elsevier Science B.V. All rights reserved.