Taking advantage of the primitive feeding characteristics of Artemia nauplii, it is possible to manipulate the nutritional value of deficient Artemia, for example HUFA deficiency in the GSL strain. Since brine shrimp nau-plii that have moulted into the second instar stage (i.e. ~8 hours following hatching) are non-selective particle feeders, simple methods have been developed to incorporate different kinds of products (HUFA, amino acids, vitamins) into the Artemia prior to feeding to predator larvae. This method of bio-encapsulation (Fig. 6.4), also called Artemia enrichment or boosting, is widely applied in marine fish and crustacean hatcheries for enhancing

Fig. 6.4 Schematic diagram of the use of Artemia as a vector for transfer of specific nutrients to marine shrimp larvae.

the nutritional value of Artemia with essential fatty acids. Currently, a variety of commercial enrichment products and procedures is available, including selected micro-algae and/or micro-encapsulated products, omega-yeast and/or emulsified preparations, and self-emulsifying concentrates and/or micro-particulate products (see review by McEvoy & Sargent 1998). Besides the enrichment diet used, the techniques employed vary with respect to pre-enrichment time (time between hatching and addition of enrichment diet), enrichment period and temperature.

Nauplii should be transferred or exposed to the enrichment medium as soon as possible before first feeding, so that they begin feeding immediately after opening of the alimentary tract (second instar stage). As a result, the increase in nauplius size during enrichment can be minimised. After 24 hours enrichment, GSL nauplii will reach about 870 p.m, and after 48 hours enrichment, about 1010 p.m (Fig. 6.5). The enrichment medium consists of hypochlorite-disinfected and neutralised seawater maintained at 25 to 28°C. Enriched nauplii are harvested after 12 or 24 hours and thoroughly rinsed using analogous procedures as after hatching (Leger et al. 1987). They are either directly fed or stored at temperatures below 10°C at densities up to 5000/ml in order to ensure that enrichment products are only slowly metabolised during storage, i.e. a reduction of 0 to 30% after 24 hours at 10°C (Fig. 6.5).

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