Detecting growth in gilthead seabream, Sparus aurata L, larvae fed microcapsules

The ability to grow Sparus aurata fed a prototype microencapsulated food in relation to larval age was examined. The contribution of live prey in co-feeding experiments (live + inert food) was also determined. To attain these objectives several feeding regimes differing in the time that inert food was introduced were tested during the first 2 weeks of larval life. Larvae fed microcapsules alone from first feeding did not increase their dry weight during the experimental period, but after the point of irreversible starvation (day 8 after hatching), the larvae were able to grow (specific growth rate 0.034) and recover their initial dry weight. The larvae fed microcapsules from day 8 or day 12, after previously being fed rotifers (from day 4 to day 8 or 12), showed similar growth rates (specific growth rate 0.053 and 0.034, respectively), although in these cases the final dry weight was higher. Survival of larvae fed only microcapsules ranged from 11%, when the capsules were added from first feeding, to over 50% when pre-fed rotifers. The addition of live prey (5% of the total food supplied on dry weight basis) improved the survival (42%) when the microcapsules were supplied from the start of feeding. Feeding incidence on microcapsules was similar to that obtained with rotifers and the physiological status of the surviving larvae at end of the experiments was acceptable. Water quality was similar between the controls fed rotifers and the treatments fed microcapsules, indicating that no negative effect on larval growth could be attributed to water quality. This study indicates that S. aurata larvae are able to grow when fed only microcapsules, although with a low growth rate probably due to a lower assimilation of the diet. Further experiments testing other sources of protein and additives are needed in order to understand the factors that are limiting larval growth. (C) 1997 Published by Elsevier Science B.V.