Effects of dietary vitamin C on fish and crustacean larvae.
In order to assess the dietary needs for ascorbic acid (AA) at startfeeding, the AA content in the various live diets currently applied in aquaculture (algae, rotifers, Artemia) was studied. Application of boosting techniques using ascorbyl palmitate (AP) as the vitamin C source enabled the transfer of elevated levels of bioactive vitamin C (up to 2500g AA.g DW-1) via the live food chain into larvae of fish (Clarias gariepinus, Dicentrarchus labrax, Scophthalmus maximus), shrimp (Penaeus vannamei) and prawn (Macrobrachium rosenbergii).
This vitamin C enrichment procedure has proven to be a valuable technique, especially for the evaluation of the effects of dietary vitamin C when supplemented at high levels, on for example stress resistance. However, for most species examined, the initial level of AA in Brachionus and Artemia impairs the determination of the minimal requirements for this component. Formulated diets containing variable levels of stable AA-phosphate esters were used for the determination of minimal requirements for AA in the early post-weaning stage of marine fish species (Dicentrarchus labrax, Scophthalmus maximus) and the postlarval stage of penaeid shrimp (Penaeus monodon, Penaeus vannamei). For both fish species examined results indicated that 20 mg AA.kg per diet is sufficient for normal growth and survival. Requirements for production of postlarval shrimp amount to minimum 20 and 130 mg AA.kg per diet, for P. monodon, resp. P. vannamei, while a level of 2000 mg AA.kg per diet is needed to enhance the resistance of the shrimp postlarvae to stress conditions and bacterial infections.
(Laboratory for Aquaculture & Artemia Reference Center, Ghent University, Rozier 44, B-9000 Gent, Belgium)
Larviculture of marine fish for sea ranching purposes: is it profitable?
In the past 15 years there has been an increased interest in sea ranching of local marine fish stocks. In the Pacific more than 30 fish species have been identified as part of a future sea ranching programme, and in the Atlantic less than 10. The programmes aim to: 1) restore depleted stocks to their 'historic' level; or 2) enhance stocks above their 'historic' level. An overall goal is to improve the local fishery, or the recreation fishery.
The present paper aims to evaluate the economic consequences in sea ranching of local marine fish stocks. Attention is given to both the yield of the local fishery and the recreation fishery. The discussion is based on the current juvenile production methods and knowledge of the biology of the species involved, present cost of released juvenile, total return rate and return rate of those released fish grown above a minimum marked size, and prices in the local fresh-fish market. The estimated break-even point is indicated in the juvenile cost. Species both from the Atlantic and Pacific waters are included.
(Institute of Marine Research, Flødevigen Marine Research Station, N-4817 His, Norway)
