OXIDATIVE STRESS IN GILL, ERYTHROCYTES, LIVER AND KIDNEY OF NILE TILAPIA (OREOCHROMIS-NILOTICUS) FROM A POLLUTED SITE

A comparison between some pro- and antioxidant parameters in erythrocy te, gill, liver and kidney of Nile tilapia, O. niloticus from a fish f arm (Control group) and from a polluted site in the Billings Reservoir (Reservoir group) was done. No hematological alterations were observe d in blood of Billings fish. The erythrocyte oxidative stress was char acterized by increased oxygen uptake and decreased induction time (ind uced by t-butyl hydroperoxide, t-BHP) evidencing a higher susceptibili ty to oxidative damage. Moreover, beside the augmented erythrocyte sup eroxide dismutase (SOD), glucose-6-phosphate dehydrogenase (G6PDH) and glutathione peroxidase activities, a decrease in both catalase (CAT) activity and total glutathione content (GSH), in erythrocytes of Reser voir fish was observed. The higher cytochrome b(5) levels observed in the gill microsomal fraction is likely to be the cause of the enhanced oxyradical production. This fact, associated with the diminished CAT and G6PDH activities, accounts for a gill oxidative stress of Reservoi r fish. Except for the NADPH-cytochrome P-450 (c) reductase activity, the other liver pro-oxidant parameters were greatly increased in the R eservoir fish. These results together with the increase in SOD activit y and decrease in CAT, glutathione reductase (GR) and G6PDH activities indicated a liver oxidative stress status. The observed increases in kidney NADH cytochrome c reductase and in both cytochromes P-450 and b (5) contents were not reflected in enhanced oxyradical production, sug gesting a well coupled P-450 catalytic cycle in this tissue. However, the antioxidant enzymes had a similar pattern in liver. The decrease i n GSH observed in kidney is probably associated with conjugation react ions for subsequent excretion. All these results furnish useful data f or future investigations of polluted aquatic sites in order to provide a data base relating the presence of pollutants to biological effects at a molecular level.