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Dependable availability of quality fry to stock grow-out production systems has been one of the most critical factors in the commercial success of industrial production of fish and shellfish. Large-scale production of marine fish fry was realized only in the last decade. Although Japan was the pioneer with the seabream Pagrus major, the most competitive hatching methods were eventually developed in Europe for the seabass Dicentrar chus labrax and the seabream Sparus aurata.

Ascorbic acid (AA) is an essential nutrient 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 µgAA/gDW), but showed a considerable variability among the different species: e.g. the concentration in Isochrysis andChlorella reached values 3-to 4-fold the percentage of Tetraselmis (0.11% of DW). Brachionus routinely cultured on Chlorella contained 2300 µg AA/gDW. Cysts of various batches and strains of Artemia differed considerably in ascorbic acid-2-sulphate (AAS) concentration (296-517 µgAA/gDW). 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 Artemia 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 µg/gDW after 24h 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 bioencapsulated 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.

Samplings were organized in three marine fish hatcheries. Samples were taken at different steps during the production of algae, rotifers and Artemia. There were 233 dominant colony types isolated for further characterization. The isolates were compared to each other and to reference strains of Phorobacrerium, Vibrio and Alreromonas, using cellular fatty acid fingerprints. Fatty acid profiles of the isolates were grouped using principal component analysis. The isolates fell into at least ten major groups, of which two correspond to the genera Vibrio and to Alteromonas, respectively. Some groups seem to be restricted to a particular type of live food or isolation site. Although 43% of the isolates belong to Vibrio, only a minority of them could be readily assigned to known species.