Effects of Lead on Respiratory Enzyme Activity, Glycogen and Blood Sugar Levels of the Teleost Oreochromis mossambicus (Peters) during Accumulation and Depuration

Abstract

Accumulation and depuration from liver and muscle were measured in Oreochromis mossambicus exposed to sublethal levels of lead (Pb) (17.5 and 35 ppm); and activities of two respiratory enzymes, as well as glycogen and blood sugar levels were studied during exposure and recovery. During exposure, a significant decline in succinate dehydrogenase (SDH) activity with a concomitant increase in glyceraldehyde dehydrogenase (GOH) activity was observed in liver and muscle, suggesting a shift in metabolism from aerobiosis to anaerobiosis. Glycogen content of liver and muscle showed a time-and dose-(P<0.01) dependent decrease, whereas blood sugar level increased. This suggests the breakdown of glycogen to glucose and mobiliza­tion to meet energy requirements. During recovery, activities of respiratory enzymes were re­versed; GOH activity and glycogen content recovered earlier than the activity of the aerobic enzyme SDH. Animals exposed to sublethal levels of Pb produced time-and dose-dependent significant increases in concentrations of Pb in liver (P<0.05) and muscle (P<0.01). On transfer of the fish to metal-free freshwater after 20 d of exposure, Pb concentrations in tested tissues gradually declined. The rate of recovery or extrapolated time between day O and 20 of recovery showed that liver and muscle completely recovered from Pb poisoning on days 54 or 82 and 44 or 62 in animals exposed to 17.5 or 35 ppm, respectively. Animals exposed to 17.5 ppm recov­ered earlier than those exposed to 35 ppm.