DIETARY ASCORBIC-ACID REQUIREMENTS DURING THE HATCHERY PRODUCTION OF TURBOT LARVAE

The effect of high ascorbic acid (AA) levels transferred through enric hed live food was evaluated for turbot Scophthalmus maximus larvae in two consecutive feeding experiments. The same feeding strategy was app lied to all treatments, except for the AA content of the live food whi ch was manipulated through bioencapsulation with ascorbyl palmitate. T his resulted finally in;a low, medium and high-AA treatment. The AA in corporation levels in the turbot larvae (up to 1400 mu g AA g DW-1) we re correlated with the AA content of the live food administered. Howev er, feeding the high AA concentration resulted in the same values as f or the medium treatment, indicating a saturation of the body AA reserv es. Under standard culture conditions, no differences in growth nor ov erall survival could be detected among the different groups, illustrat ing that the dietary AA requirements of larval turbot are met by non-e nriched live food containing already 500 mu g AA g DW-1. The larvae of the high-AA treatment, however, showed a better pigmentation rate (47 and 32% for experiments 1 and 2, respectively) compared to the other groups (35 and 25%, respectively). Evaluation of the physiological con dition applying a salinity stress test revealed an improvement by feed ing extra AA, significantly in the medium-AA treatment. Though not sig nificantly different, cumulative mortalities after challenge with Vibr io anguillarum amounted to 50% for the control v. 40% for the fish fed medium and high-AA diets, respectively. Moreover, the onset of mortal ities in this study was slower (not significantly) for the fish fed th e extra AA. (C) 1996 The Fisheries Society of the British Isles