THE EFFECT OF DIETARY EXOGENOUS DIGESTIVE ENZYMES ON INGESTION, ASSIMILATION, GROWTH AND SURVIVAL OF GILTHEAD SEABREAM (SPARUS-AURATA, SPARIDAE, LINNAEUS) LARVAE

The success of microdiets commonly used in the cultivation of marine fish larvae is limited to serving as partial replacements for live food. This limited success is thought to be associated with a reduced digestive ability due to an incompletely developed digestive system. The enhanced growth obtained from live food has been partially attributed to the digestive enzyme activity of the food organism. The present study was designed to test the effect of an exogenous digestive enzyme incorporated into a microdiet on the growth of Sparus aurata. Larval gilthead seabream, 20-32 days old, were fed C-14 labelled microdiets containing a commercial pancreatic enzyme at different concentrations (0, 0.1 and 0.05 g/100 g dry diet). Rates of ingestion and assimilation were measured and their relationship to dry weight was determined. Our results show that the success of the microdiet as a food for larval gilthead seabream was limited by the larva's low ingestion rate which only approached its maintenance requirement. In addition, the presence of digestive enzyme in the microdiet enhanced its assimilability by 30%. Larval growth over ten days was 0, 100 and 200% on microdiet free of added enzymes, one with added enzymes and a live food regime, respectively. It is our opinion that successful development of microdiets for Sparus aurata must be based on diets improved both in digestibility and attraction to the larvae. Further studies are now underway to determine the nutritional requirements of gilthead seabream larvae using the experimental method developed in the present study.