VARIATION OF ASCORBIC-ACID CONTENT IN DIFFERENT LIVE FOOD ORGANISMS

Ascorbic acid (AA) is an essential nutrient both in particle and live aquafeeds. In order to better assess the needs for this nutrient during larviculture the AA content of algae, rotifers and Artemia was studied with respect to their suitability at startfeeding. In general, the microalgae evaluated were rich in AA ( 1000-4000 mu g AA/g DW),but showed a considerable variability among the different species: e.g. the concentration in Isochrysis and Chlorella reached values 3-to 4-fold the percentage of Tetraselmis (0.11% of DW), Brachionus routinely cultured on Chlorella contained 2300 mu g AA/g DW. Cysts of various batches and strains of Artemia differed considerably in ascorbic acid-2-sulphate (AAS) concentration (296-517 mu g AA/g DW). The amount of AA available in the freshly-hatched nauplii reflected exactly the AAS reserve present in the cysts, what evidences the complete conversion of AAS to free AA during completion of embryonic development into nauplii. Boosting techniques both for Brachionus and A rtemia using ascorbyl palmitate (AP) as the vitamin C source were established. The addition of 20% AP in the diet of Brachionus enhanced their AA content 10-fold over 3 days of culture. Supplementation of the enrichment emulsion for Artemia with 20% AP increased the AA content up to 2000 mu g/g DW after 24 h enrichment. This lipophilic derivative of AA appeared to be a stable form of vitamin C for enhancing AA levels in the live diets during culture and/or enrichment. This bioencapsulation method provides a tool for hatcheries to build up high AA concentrations in the live prey administered to first feeding larvae of aquaculture organisms in case of specific requirements (e.g. with respect to handling stress, deformities). A survey of commercial hatcheries indicated that a wide range of products is used for the cultivation and boosting of rotifers, which consequently affect their AA levels. In general, the AA content in the algae and, consequently, the algal enrichment of Brachionus tended to score lower in the hatcheries than under lab conditions.