ANTIOXIDANT DEFENCE IN THE EARLY LIFE PHASE OF BROWN TROUT Salmo trutta

Aquatic organisms including fish are prone to oxidative stress as they are rich in polyunsaturated fatty acids (PUFAs) which have important physiological functions especially in cellular membranes. Generation of radical oxygen species (ROS) is a natural consequence of aerobic metabolism and it becomes more critical during the early development of fish due to the rapid tissue growth resulting in high oxygen consumption.  Therefore, free radical damages may reduce survival during the early development thence recruitment in natural fish stocks. The present study was conducted as the first to evaluate the changes in lipids, fatty acids and antioxidant defense system during the early development of wild brown trout (Salmo trutta).  Eggs obtained from the Stream Yagli (Coruh Basin, Turkey) were fertilized and incubated at 9.5^oC until the swim-up stage.  Total lipids dramatically decreased from 9.3% (egg) to 4.3% (swim-up) with a main decrease in neutral lipids. Docosahexaenoic acid (DHA; 22:6n-3) was the predominant fatty acid in all cases and was preferentially protected during the early development. Molecular antioxidant scavengers such as vitamin E, C and B1were allocated to the eggs at an abundant level and they decreased dramatically after hatching while the activities of antioxidant enzymes such as catalase (CAT), superoxide dismutase (SOD) and glutathione S-transferase (GST) increased at the same circumstance. Our overall results suggest that high level of non-enzymatic free radical scavengers detoxify ROS during the embryonic development and elevated antioxidant enzymes take this duty over after hatch, protecting embryos and fries from oxidative stress.