Modulation of calcium uptake in cadmium-pretreated tilapia (Oreochromis mossambicus) larvae

Tilapia larvae were exposed to 0 (control), 50 (50-Cd) or 100 (100-Cd) mu g l(-1) cadmium for 4 days and then transferred to cadmium-free fresh water for 3 days of detoxification. Total length and weight, calcium influx and total body calcium and cadmium content were examined at various times during detoxification. All the groups grew normally with regards to total length and body weight. Within the first 12h of detoxification the 50- and 100-Cd exposed groups released cadmium at the similar rate of about 24 ng mg(-1) h(-1) (or 140 ng larva(-1) h(-1)). Later, however, this rate declined to only 4-16% of the initial level. Calcium influx in the control group showed a 10-26% increase during the detoxification period. Calcium influx in the 50-Cd group increased by about 280% and reached its peak at 12h. Calcium influx in the 100-Cd group increased by 440% and did not peak until 24h after transfer. After peaking, the influxes in both 50- and 100-Cd groups declined to the level of control at the end of the experiment. Calcium contents in 50- and 100-Cd groups increased more rapidly than that in control group within first 24h of the detoxification period. However the rate of increase in calcium content in three groups was the same after 24h. The changes in calcium influx appeared to be correlated with those in calcium content, and these suggested that tilapia larvae regulate the mechanism of calcium balance to compensate for the reduced calcium level in the body.