Broodstock management and nutrition and egg and larval quality in the Atlantic halibut (Hippoglossus hippoglossus) and European seabass (Dicentrarchus labrax)

Abstract

Commercial aquaculture for marine species is gaining importance in todays industry. Over fishing of the natural recource has sadly meant that many of the higher predators halibut, turbot, seabass, sea bream and tuna are now financially suitable for the industry. This thesis covers a wide range of topics involving two of the most valuable marine species, namely the Atlantic halibut and European seabas, from broodstock to larval first-feeding. Broodstock husbandry and especially nutrition are often the last to receive attention. This study shows that careful management of the broodstock, firstly by the close timing of stripping, secondly enhancement of the broodstock diet with n-3 and n-6 HUFA can increase both fecundity and egg quality right up to the point where the larvae switch from endogenous to exogenous feeding. The implications for the industry for these two species are twofold. Firstly, The identification that halibut eggs can be fertilised within 6 hours of ovulation with no detrimental effects on fertilisation rates and subsequent egg performance means that eggs could be transported to specialist egg and larval rearing units. Thus the potential exists for the industry to be divided into separate units dealing with different stages of the life cycle much like the salmon industry. Secondly, the development of an artificial pelleted brood stock diet would mean that problems of consistency and quality and also the dangers of disease infection via the feed can be removed from broodstock management. The stage of first-feeding for halibut is still considered to be the main bottleneck in the production of this species. The current work has shown that small systems of 100-1 can be used to successfully rear halibut larvae. Although careful consideration must be made of the system design to ensure that predator (larvae) and prey (Artemia) remain homogeneously dispersed. Also, the need to use rotifers at first feed has been shown to be unecessary. However, nutrition of first-feeding larvae still requires the use of wild zooplankton to ensure successful pigmentation. Yet, Artemia supplied with commercial enrichments still perform adequately in terms of their overall growth.