Variation in the absorption of macromolecular proteins in larvae of the sea bassDicentrarchus labrax during transition to the exotrophic phase

Absorption of proteins by pinocytosis was studied in the postvalvular intestine of larvae of the sea bassDicentrarchus labrax during transition to the exotrophic phase. Comparison of specimens ranging in age from 4 or 5 d (age of mouth opening) to 25 d (period of strictly exotrophic feeding) made it possible to determine the morphofunctional development of enterocytes when fish are fed onArtemia sp. (Brazil strain). The pinocytotic activity of enterocytes was weak at the time of mouth opening, but intensified rapidly. After the first feed (7 to 8 d), enterocytes were capable of absorbing proteins, since they actively incorporated ferritin. At the age of 18 to 19 d, they showed a strong capacity for absorption resulting in the formation of a large supranuclear vacuole by the age of 25 d. Examination of the intestine of larvae fed artificially showed that enterocytes developed little until 18 to 19 d of age, but the presence of supranuclear vacuoles in the cytoplasm nevertheless indicated a capacity for absorption.