Abeer Ghazie Azize Al-sawafi, Lixiao Wang and Yunjun Yan
Acute toxicity of cadmium (Cd) to zebrafish (Danio rerio) was studied. The 24, 48, 72 and 96 h LC50 values (with 95% confidence limits) estimated by probit analysis were 16.73 (20.03-13.98), 12.88 (14.96-11.08), 11.46 (13.21-9.94), 9.68 (11.12-8.43) mg L-1, respectively. To determine the accumulation and cyto-toxicity of Cd on the brain and skeletal muscle of zebrafish, specimens of zebrafish were exposed to three concentrations of cadmium (0.65 mg Cd L-1, C1; 0.97 mg Cd L-1, C2; and 1.94 mg Cd L-1, C3 (corresponding to 1/15th, 1/10th and 1/5th of 96 h LC50), respectively for 25 days. The concentration of Cd in the fish tissue was detected by Inductively Coupled Plasma Mass Spectrometer (ICP-MS). Tissue alterations of brain and skeletal muscle were observed under light microscope. Cadmium concentrations of the treated fishes showed a significantly exponential increase over time and peaked at Day 25. In term of histomorphology of brain and skeletal muscle, obvious tissue chaos was noticed in the treated fishes compared to the control group. This mess clearly appeared at Day 25 at C3 in the brain where the tissue showed different extents of granule cell loss, degeneration of Purkinje cells, aggregation area of gliosis and many areas of necrosis. Ultra-structural damage of moderate or low levels was observed in the fishes at C1 and C3 after 5 days and C1 after 25 days of treatment. In the skeletal muscle at 25 days of C3 treatment, different degrees of swelling and high necrosis were observed. This indicates that a defense mechanism was started with the accumulation of metal Cd in the tissues over time. Thus, the information provided in this study may be very useful for the deep understanding of the mechanisms of Cd stress in fish.
