Towards an inert diet for first-feeding gilthead seabream Sparus aurata L.larvae

The development of an inert food to replace live prey during the early stag es of marine fish larvae requires research in different fields and therefor e a precise work strategy. Our research on this subject has been carried ou t in successive steps using the gilthead seabream Sparus aurata. The first step was the design of a food particle that would be well accepted and inge sted by free-swimming marine larval fish during the first developmental sta ges. We chose microencapsulation by polymerization of the dietary protein a s the most appropriate method for making the particles; different types of microcapsules were made using a basic diet containing only the major dietar y components. In the second step, our aim was to keep the larvae alive in a routine rearing system in 300-L tanks, using exclusively this kind of food , long enough to detect any changes in growth, survival, or anatomical and histological status of the larvae, in order to verify whether the technolog ical changes were positive. The third step focused on diet formulation and searching for clues to inefficient assimilation and growth. The use of 'in vitro' digestibility techniques allowed us to detect the inhibitory effect of some diet ingredients on larval proteases and to determine more suitable sources of protein. We now have a microcapsule able to efficiently support growth and development of S. aurata larvae, at least during the first 2 we eks of life, although the larvae still need to feed on rotifers during the first 2-4 days of exogenous feeding. This microcapsule will make it possibl e to make advances in determining the specific nutritional requirements of larval fish.