CAPACITY OF GILTHEAD SEABREAM, SPARUS-AURATA L, LARVAE TO BREAK DOWN DIETARY MICROCAPSULES

The capacity of hatchery-reared gilthead seabream larvae to disintegrate mixed-walled protein/carbohydrate microcapsules in their midgut was studied. The response of feeding larvae to eight types of microcapsules was examined. The effects of the following factors, which could potentially influence capsule breakdown, were evaluated: (a) larval age; (b) addition of enzymes to the diet; (c) concentration of cross-linking agent; and (d) procedure for isolating microcapsule after formation. The results revealed that larvae belonging to the same population exhibited substantial individual variability in their capacity to disrupt the microcapsule wall. Despite this, there were clear differences in the ability of the larvae to break down different types of microcapsules, depending principally on the technique followed during the isolation phase of microcapsule elaboration. Thus, capsules isolated in gelatin (type G) were more easily broken down than those isolated in alcohol (type A), irrespective of larval age (P < 0.001), Addition of enzymes to capsules did not result in any significant changes (P > 0.05) in the degree of capsule breakdown. Likewise, the concentration of cross-linking agents used to form the capsule walls had no effect on capsule disruption by the larvae. The present results suggest that seabream larvae are able to digest inert food from the onset of exogenous feeding. Their capacity to do so is, however, influenced by the thickness of the capsule coating and by their age. The results of this study also contribute to our knowledge of the behaviour of a cultured larval population in the presence of microencapsulated food.