Correlation between metallothionein and energy metabolism in sea bass, Dicentrarchus labrax, exposed to cadmium

Specimens of sea bass (Dicentrarchus labrax) were exposed to two different cadmium concentrations (0.5 and 5 mu g Cd2+/ml seawater) for a period of 7 days, Cadmium accumulated in the tissues of D. labrax in the following order: kidney > liver > gills at both concentrations. Accumulation patterns in fish exposed to 0.5 mu g Cd2+/ml seawater were different with respect to 5.0 mu g Cd2+/ml seawater. At both Cd concentrations a similar stress situation occurred during the first 4 hr as noted by the depletion of glycogen stores and the increase in free glucose in the muscle; metallothionein was induced in the liver, but failed to bind all the cytosolic Cd, which was in part bound to high-molecular-weight ligands. Fish recovered from this initial stress situation within 24 hr as indicated by the increase in glycogen and the decrease of glucose. Long-term effects were clearly dependent upon metal concentration: at lower Cd exposure, metallothionein induction increased linearly with time and counteracted the toxic effect of the metal; on the other hand, when fish were exposed to 5.0 mu g Cd2+/ml seawater a clear stress occurred at the end of the exposure, as indicated by the notable decrease of glycogen stores, the increase of free glucose, the decrease of AEC in the muscle and the increase of Cd bound to high-molecular-weight ligands in the liver.