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 durin g larviculture the AA content of algae, rotifers and Artemia was studi ed with respect to their suitability at startfeeding. In general, the microalgae evaluated were rich in AA ( 1000-4000 mu g AA/g DW),but sho wed a considerable variability among the different species: e.g. the c oncentration in Isochrysis and Chlorella reached values 3-to 4-fold th e percentage of Tetraselmis (0.11% of DW), Brachionus routinely cultur ed on Chlorella contained 2300 mu g AA/g DW. Cysts of various batches and strains of Artemia differed considerably in ascorbic acid-2-sulpha te (AAS) concentration (296-517 mu g AA/g DW). The amount of AA availa ble in the freshly-hatched nauplii reflected exactly the AAS reserve p resent in the cysts, what evidences the complete conversion of AAS to free AA during completion of embryonic development into nauplii. Boost ing techniques both for Brachionus and A rtemia using ascorbyl palmita te (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 Artemi a 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 cul ture and/or enrichment. This bioencapsulation method provides a tool f or hatcheries to build up high AA concentrations in the live prey admi nistered to first feeding larvae of aquaculture organisms in case of s pecific requirements (e.g. with respect to handling stress, deformitie s). A survey of commercial hatcheries indicated that a wide range of p roducts is used for the cultivation and boosting of rotifers, which co nsequently affect their AA levels. In general, the AA content in the a lgae and, consequently, the algal enrichment of Brachionus tended to s core lower in the hatcheries than under lab conditions.