Preliminar studies on proteolytic digestive enzimes in the larval and juvenile stages of the mullet Mugil platanus Günther, 1880 (Osteichthyes, Mugilidae)

Abstract

Functional development of the digestive system in larval to young stages of the mullet Mugil platanus was studied through activity analysis of proteolytic enzymes. Fishes from 4 to 29 days old and 1 year old were reared in Mariculture laboratories of the Instituto de Pesca. The enzymatic activity of crude extracts obtained from larvae, whole digestive tract of 1 year old mullet, rotifers and Artemia nauplii were measured in a spectrophotometer. Trypsin and carboxypeptidases A and B activity occurs since the beginning of the exogenous feeding, while pepsin and chymotrypsin were detected only in juveniles. The enzymatic activity found in rotifers and Artemia sp. was at the same or upper level than in larvae, showing that the exogenous enzymes can take an important role in the early development of the fish. Food ingestion induced an increase of enzymatic activity in juveniles. The low proteolytic activity presented during the initial larval stage makes difficult to replace live food by artificial diets in those stages. Research should be done on developing diets with previously hydrolyzed proteins or free aminoacids as well as to determine the viability to incorporate purified enzymes in the manufactured diets for the young larvae.