Relationships between antioxidants, antioxidant enzyme activities and lipid peroxidation products during early development in Dentex dentex eggs and larvae

The overall aim is the characterization of the antioxidant systems in marine fish during early development in order to enhance growth and quality of early life stages by avoiding oxidation problems that may cause pathologies and disease. The present study determined the activities of the antioxidant system enzymes and levels of vitamin E, lipid peroxidation products and fatty acids during early development without exogenous feeding in the marine fish, Dentex dentex. Samples of fertilized eggs just prior to hatch, newly hatched larvae and unfed larvae up to day 9 after hatch were analysed on a daily basis. The larvae did not grow during the experiment and by day 9 the surviving larvae weighed only a third of the newly hatched larvae. Lipid was a major energy source during this period of starvation as evidenced by greatly decreased amounts of total lipid due to a preferential utilisation of neutral lipids. All groups of fatty acids (saturated, monounsaturated and polyunsaturated) were consumed throughout the starvation period. Vitamin E levels were relatively constant until significantly declining by days 8 and 9. Similarly, levels of lipid-soluble fluorescent products (LSFP) were relatively constant until day 6 and then significantly decreased from days 7 to 9. In contrast, the level of malondialdehyde (MDA) was very high in eggs but was 3-fold lower in newly hatched larvae and then decreased over the whole time-course and was also significantly lower on days 8 and 9. The activities of enzymes of the antioxidation system were expressed in both eggs and early larvae and varied during the developmental period with levels of catalase and glutathione peroxidase (GPX) being initially low in eggs whereas glutathione-S-transferase (CST) and superoxide dismutase (SOD) were higher in eggs than in larvae. Overall, the activities of catalase and GPX increased, whereas GST and total SOD activities decreased, during the early stages of development during a period where there was no exogenous dietary input into the larvae. Glutathione reductase activity was very low and showed an increasing trend initially until days 2-3 before declining and varying over the remaining period. In conclusion, we determined the prooxidant (polyunsaturated fatty acid) status. antioxidant status (vitamin E), peroxidation status (MDA and LSFP) and the activities of the antioxidant enzyme systems in a single integrated study in unfed marine fish larvae during early development.