Bioaccumulation of cadmium and its cytotoxic effect on zebrafish brain

In order to study the accumulation and cytotoxicity of cadmium (Cd) in the brain of zebrafish (Danio rerio), specimens were exposed for 16 days to 1.0 mg · L−1 of CdCl2 and the brains were analysed at 2, 7 and 16 days of treatment. The concentration of Cd in the brains was detected by atomic absorption spectrometry; tissue alterations were revealed under light and electron microscopes. Cadmium concentrations in the brain of treated fish appeared to increase exponentially over time, reaching a peak at 16 days. As regards brain histomorphology, we observed evident tissue disorganisation in treated fish compared with control specimens. This disorganisation appeared particularly at 16 days in the optic tectum, in the ventricle area where the ependymal cells appeared sparsely distributed and in the medulla oblongata. Moderate ultrastructural damage was observed in the fish at 7 days of treatment. In the brain at 16 days of treatment, we observed considerable mitochondrial swelling with a loss of cristae, and several cells showed large autophagic vacuoles. This is indicative of a defence mechanism which occurs over time and in parallel with the accumulation of metal in the organ.