Background. Fish are the principal source of n-3 and n-6 fatty acids for humans. Traditionally, these fatty acids have been supplied in the form of captured marine and freshwater fishes. Recently, freshwater cultured species have been increasing their share in the fish volume on the market. Therefore it is crucial for fish farmers to rear fish under proper condition and with proper feeding in order to receive good quality fish flesh at harvest. The presently reported study was aimed at determining the effect of diet with the increased level of lipids or carbohydrates on selected blood indices, reduced glutathione content, lipid peroxidation products concentration in the liver, and body weight gains in carp fingerlings reared in post-cooling waters. Materials and methods. The experiment was carried out in spring (2004) on 300 carp divided into two feeding groups. Group I was fed high-fat feed, whereas group II high-carbohydrate feed. After 7 weeks, fish blood and livers were collected for further analyses. Results. Significantly higher body weight gains were found in the fish fed high-fat feed as well as significant increase of haemoglobin (Hb) concentration in the blood of both feeding groups, which was accompanied by the increase of haematocrit (Ht) index. Furthermore, an increase in the concentration of lipid peroxidation products was observed as well as significantly lower content of reduced glutathione (GSH) in the livers of fish examined. Conclusion. The observed MDA values and reduced glutathione (GSH) concentration in the fish liver may indicate enhanced peroxidation processes in the organisms of the fish from both experimental groups, caused by their intensive feeding with extruded feeds. The peroxidation processes were more intensive in fish fed high-fat feeds.

fish, carp, Cyprinus carpio, haemoglobin (Hb), haematocrit (Ht), reduced glutathione (GSH), lipid peroxidation products (MDA), breeding, nutrition