Metallothionein induction in early larval stages of tilapia (Oreochromis mossambicus)

Amounts of whole-body metallothionein (MT) in tilapia (Oreochromis mossambi cus) larvae increased to a peak (1,500 ng mg(-1) protein) 1 d after hatchin g (H1), decreased rapidly thereafter, and was maintained at a constant leve l (700 ng mg(-1)) 3 d after hatching (H3). Waterborne Cd2+ could stimulate MT expression in newly hatched (H0) larvae in dose-dependent and time-depen dent patterns. H0 larvae, which were treated with 35 mug L-1 Cd2+ for 24 h, showed a 1.7-fold increase in the MT amount (174.0 +/- 64.7) and a 6.5-fol d increase in accumulated Cd2+ but no significant change in Ca2+ content, c ompared with the H0 control (MT, 102.6 +/- 48.1). H3 larvae with the same t reatment revealed about a 10-fold increase in accumulated Cd2+, a 10% decre ase in Ca2+ content. but no change in MT (261.2 +/- 120.0), compared with t he H3 control (MT, 330 +/- 74.0). H0 larvae could synthesize more MT to bin d Cd2+ for detoxification in 35 mug L-1 Cd2+, a dose that would not affect normal physiology or survival of H0 larvae. On the other hand, 35 mug L-1 C d2+ caused H3 larvae to experience hypocalcemia, an abnormal physiological condition, in which H3 larvae could not synthesize sufficient MT, thus caus ing greater than 25% mortality. These results indicate for the first time t hat the inducibility of MT by waterborne Cd2+ is development dependent, bei ng correlated with inconsistent sensitivities to Cd2+ during larval develop ment.