The potential toxicity of silver nanoparticles (AgNPs) to the early stages of fish is still unclear. This study used zebrafish embryos as a model to investigate the toxic effects of AgNPs on ion regulation by skin ionocytes. Zebrafish embryos were exposed to AgNPs for 96 h (4–100 h post-fertilization (hpf)) or 4 h (96–100 hpf). After 96 h of exposure to 5 and 10 mg/L AgNPs, survival rates had decreased to 42% and 0%, respectively; the body length had also significantly decreased at 5 mg/L. Whole-body Na+ and K+ contents significantly decreased at 1 and 3 mg/L, while Ca2+ contents decreased at ≥0.1 mg/L. H+ secretion by the skin significantly decreased at 1 mg/L. The density of skin ionocytes labeled with rhodamine 123 (a mitochondrion marker) decreased by 25% and 55% at 1 and 3 mg/L, respectively; and 54% of ionocytes (at 3 mg/L) were deformed from an oval to a spinous shape. After 4 h of exposure to 1 and 5 mg/L, whole-body Na+ and Ca2+ contents, H+ secretion, and density of ionocytes had also significantly decreased. This study revealed the toxicity of AgNPs to skin ionocytes and ion regulation in the early stages of zebrafish embryos.
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