Marleen Dehasque

Variation of ascorbic acid content in different live food organisms.

Abstract 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 μg 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 μg AA/g DW. Cysts of various batches and strains of Artemia differed considerably in ascorbic acid-2-sulphate (AAS) concentration (296–517 μg 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 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/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.

An oral challenge for turbot larvae with Vibrio anguillarum

M. Chair 1, M. Dehasque 1, S. Van Poucke 2, H. Nelis 2, P. Sorgeloos ~* and A.P. De Leenheer 3 1 Laboratory of Aquaculture and Artemia Reference Center, University of Ghent, Rozier 44, B-9000 Ghent, Belgium 2Laboratory for Pharmaceutical Microbiology, University of Ghent, Hare/bekestraat 72, B-9000 Ghent, Belgium 3Laboratory of Medical Biochemistry and Chemical Analysis, University of Ghent, Harelbekestraat 72, B-9000 Ghent, Belgium

Communications: Bioencapsulation of the Antibacterial Drug Sarafloxacin in Nauplii of the Brine Shrimp Artemia franciscana

Abstract Nauplii of the brine shrimp Artemia franciscana were enriched with the antibacterial drug sarafloxacin hydrochloride to determine if levels effective against four pathogenic strains of Vibrio spp. would accumulate in brine shrimp. Three vibrio strains were Vibrio anguillarum; the fourth was V. vulnifcus. Concentrations of sarafloxacin ranging from 1 to 40% (weight volume) were incorporated into the oil phase of Super Selco brine shrimp diets. Enriched nauplii and controls were sampled at 2-h intervals for 24 h. Antibiotic sensitivity testing was evaluated with a modification of the Kirby–Bauer disk diffusion method. A microbiological assay with Escherichia coli was used to determine the concentration of sarafloxacin per sample of nauplii. The results indicate that sarafloxacin is rapidly taken up by larval brine shrimp and can be detected at 2 h of enrichment by microbiological assay. The efficacy of sarafloxacin appears to depend on the strain of pathogen present.

Vaccination of European sea bass fry through bioencapsulation of Artemia nauplii

European sea bass (Dicentrarchus labrax) fry vaccinated orally via bioencapsulation in Artemia nauplii or by bath method exhibited better performance than control fish in terms of growth, food conversion and resistance to stress. The comparable survival between vaccinated and non-vaccinated animals suggests that vaccination methods are not stressful. The present study shows that oral vaccination can be used to enhance growth in fish fry.