Egg quality in marine fishes

For commercial fry production in fish the determination of egg quality is important to guarantee product quality and maintain hatchery efficiency, to improve methods for fry production and for brood stock maturation. Egg quality determination is possible for fresh water fish and there exist some simple and quick assays predestinated for practical use. Not only because of biological differences but also because of differences in the techniques for fly production and gamete collection the quality assays developed for eggs of fresh water fish are not adaptable for marine fish. However, because of the above mentioned reasons reliable assay methods would be also very important in mariculture. Therefore the proposed project has the intention to develop assays for the determination of egg quality in marine fish during routine fry production. It uses the sea bream (Sparus auratus) as model as it is one of the most important cultured species, and the data can be transferred to several closely related and also commercial important sparid species (Pagellus sp., Diplodus sp., Dentex sp). First basic research on morphological, physiological, and biochemical parameters of the eggs and their changes during activation, and early development is performed. On basis of these data parameters are selected which are supposed to be suitable for egg quality determination. Using individual and artificially inseminated egg samples the parameters are tested on their relation to the survival rate of developing eggs in the 4 cell stage, of embryos in the stage with free tailbuds and clearly differentiated somites, larvae in the flexion stage and juvenile fish just after metamorphosis. On basis of these data a further parameter selection is performed and the most suited ones are tested for screening the egg quality during routine fry production. Additionally changes in egg quality during the course of a spawning season and during the diurnal spawning rhythm are investigated.

The conducted project investigated parameters which are useful to predict the egg quality in two marine fish species (gilthead seabream - Sparus aurata, and sharpsnout seabream - Diplodus puntazzo). The term egg quality describes the proportion of eggs in an egg batch which successfully complete development to the larval stage. In fish culture egg quality determination is important for the production of healthy and high quality fish larvae and for economical utilization of hatcheries. It is necessary in species which have recently been introduced in culture and for which reproduction techniques are still in development, namely for many marine fish. Egg quality should be predicted with parameters measured in unfertilized eggs or eggs in early development stages. Biochemical, physiological and morphological parameters of eggs were investigated. While the physiological parameters were not suited to define the egg quality it was possible with biochemical and morphological parameters. Concerning the biochemical parameters, it was found that carbohydrate metabolism is essential for normal egg development and that several enzymes and metabolites belonging to these pathways are correlated with egg quality. Based on the mentioned carbohydrate parameters regression models could be formulated which can predict the egg quality with a high statistical significance. In comparative studies it could be demonstrated that carbohydrate metabolism was also essential for developing eggs of fresh water fish and correlated with egg quality, too. These are completely new results. Until now the importance of carbohydrate metabolism for developing teleost eggs was underestimated and amino acid metabolism was considered as most important. Concerning the investigated morphological parameters it was found that the shape of the lipid vesicle is a quality marker for eggs of Sparus aurata and Diplodus puntazzo. As the determination of this parameter bases on the measurement of the maximal and minimal diameter of the lipid vesicle, the assay is very simple and rapid, does not require special knowledge and measurement can be automated by computer programs. This is an advantage in comparison to biochemical methods which are more elaborative and more cost intensive. Therefore the assay it is one of the most promising which exists for egg quality determination in teleost fish.