Effects of embryonic exposure to polychlorinated biphenyls on zebrafish (Danio rerio) retinal development.

Polychlorinated biphenyls (PCBs) are persistent environmental pollutants that affect embryonic development. The purpose of this study was to examine the effects of embryonic exposure to PCBs on early retinal development in zebrafish, Danio rerio. Zebrafish embryos were immediately exposed to different concentrations (0, 0.125, 0.25, 0.5, 1.0 and 2.0 mg) of PCBs per liter of medium at 28.5 °C. Embryos were assessed at 30, 48, 72 and 96  h post-fertilization (hpf) for changes in embryonic survival rate, development, larval retinal morphology and ultrastructure of the retina. The results show that PCB exposure decreased the survival rate of embryos in a time- and dose-dependent manner. Embryos exposed to the higher concentrations of PCBs (0.5, 1.0 and 2.0  mg l(-1) ) displayed obvious gross morphological deformities. At 72  hpf, the retinal layer development of zebrafish was delayed at higher PCB concentrations (1.0  mg  l(-1) ). At 96  hpf, irregularity of photoreceptor cells arrangement and thickening of photoreceptor and ganglionic layers were observed in PCB-treated larvae at concentrations of 0.25-1 mg  l(-1) . Ultrastructural examination showed signs of growth inhibition of the photoreceptor outer segment at 0.25-1 mg  l(-1) PCB exposure at 72  hpf, as well as the appearance of massive vacuoles and holes inside the outer segments in the PCB exposure group at 96  hpf. These results suggest that embryonic exposure to moderate and high levels of PCBs induced developmental deficits in zebrafish retinas, particularly in photoreceptor cells.