Variation in egg and larval quality in various fish and crustacean species

It is generally accepted, that a major constraint in the further development of marine fish and crustacean aquaculture, is the variable quality of eggs and larvae used for the hatchery-production of fry. Nonetheless, valid criteria to evaluate optimal egg quality have not been identified yet. Instead, particular indicators, are used, e.g. the fertilization and hatching rate, overall culture success during the first rearing period, etc., but these are not totally objective because hatchery-specific conditions may interfere. The biochemical composition of the egg may be one of the possible determinants of egg quality, which can be evaluated on a more objectie basis. In this respect, studied have been initiated to analyze in freshly-released eggs, the levels of two nutrients which are believed to play a critical role in the early larval development, i.e. (n-3) highly unsaturated fatty-acids (HUFAs) and vitamin C. Analytical data have been gathered for various species of marine fishes (Scophthalmus maximus, Epinephelus tauvina and E. fuscoguttatus, Dicentrarchus labrax, Sparus aurata, and Pagrus major) and for the freshwater prawn (Macrobrachium rosenbergii). Egg samples have been collected from wild females and from captive broodstock kept under various conditions at various hatcheries. Results available so far illustrate that for some of the species tested HUFA levels and total lipid content in the eggs vary considerably among spawnings, even when coming from the same hatchery. The highest variation was noted in turbot broodstock, i.e. the HUFA levels and total lipid content ranged from 19 to 47 mg/g DW, and 8 to 30%, respectively. Contents of ascorbic acid in turbot eggs varied up to 100%, respectively 500% among different egg batches provided by two hatcheries.