Towards the development of suitable microdiets for substitution of live prey in the rearing of red drum (Sciaenops ocellatus) larvae: Applications of studies on digestive physiology

The digestive capacity of red drum larvae during ontogeny was assessed using histological, biochemical and molecular techniques in an attempt to reduce the need for live prey during rearing. Based on the our previous studies of the differentiation of the digestive tract and associated organs, and this study's characterization of the proteolitic digestive enzymes, it was concluded that the digestive system of red drum is highly functional at first feeding. Enzymes for the digestion of proteins were present before exogenous feeding commenced. Alkaline proteases had a higher relative contribution early in development, and presumably played a major role in digestion. Acid proteases became more important toward the end of the larval period, concomitant with the development of a functional stomach. Results obtained through the characterization of digestive enzymes were utilized to develop in vitro assays to measure protein digestibility in order to select adequate protein sources. Based on these results, microdiets were developed which included intact protein sources and protein hydrolysates.