DIFFERENT SENSITIVITIES TO CADMIUM IN TILAPIA LARVAE (OREOCHROMIS-MOSSAMBICUS TELEOSTEI)

The Cd toxicity, its accumulation and effects on the development and t he tissue water and cation contents of tilapia larvae (Oreochromis mos sambicus) were studied. Both 96-h LC(50) and the accumulation rate hav e dramatic changes following larval development and reveal an inverse relation: LC(50) of 0-(newly hatched), 1-, 2-, 3- and 7-day-old larvae were 205, 83, 33, 22 and 29 mu g/L, respectively, while their accumul ation rates were 1.06, 2.64, 2.94, 4.94 and 2.70 ng/larva/day, respect ively. Different accumulation rates explain the dramatic changes in LC (50) during the early larval stages of tilapia. Exposure to 200 mu g/L Cd for 4 days caused a significant decrease in both total length and yolk absorption of tilapia larvae, while the effect of 50 mu g/L Cd wa s not significant, i.e., a high dose of Cd inhibited the development o f tilapia larvae. At the end of four days, 0-day-old larvae exposed to 200 mu g/L Cd accumulated less than those exposed to 50-100 mu g/L, p ossibly due to the inhibition of larval development caused by a higher Cd level. Exposure to 100 or 200 mu g/L Cd for 4 days induced a signi ficant decrease in the contents of water, Ca2+, and K+ in larvae. Howe ver, there was no change in the concentrations of Na+ and Mg2+. The im pact of a higher level of Cd on the ion and water balance in larvae ma y be one of the lethal effects of Cd to tilapia larvae.