Ef fects of Dieldrin on Life Stages of the African Catfish,Clarias gariepinus(Burchell)

Early life stages ofClarias gariepinuswere found to be less sensitive to acute dieldrin toxicity than were those of Nile tilapia,Oreochromis niloticus; 96-h LC50values for 37-day-old fry were 11.7 and 4.95 μg liter−1, respectively. The growth ofC. gariepinusfry was unaffected by 30 days of exposure to 2.4 μg liter−1dieldrin under static conditions with water renewal every 96 h, whereas growth ofO. niloticusfry was significantly reduced. AdultC. gariepinusexposed to dieldrin for 30 days, with water changes every 96 h, rapidly absorbed dieldrin from aqueous solution. Dieldrin concentration was measured just before water changes and from an initial concentration of 4.0 μg liter−1, stabilized after 12 days at about 0.075 μg liter−1, indicating that a balance between uptake and excretion and metabolism had been achieved. Dieldrin accumulated in the tissues during these exposures, especially in the liver, where after 30 days the bioconcentration factor relative to initial concentration was about 900. Chronic exposure ofC. gariepinusto dieldrin had no effect on blood hematocrit and hemoglobin, but appeared to slow the growth of catfish and had a clear negative effect on the reproductive potential of mature females.