Developmental toxicity of copper in marine medaka (Oryzias melastigma) embryos and larvae

Copper as developmental toxicants have been reported extensively in freshwater fish, however, the sublethal and chronic toxic effects of Cu to the early life stages of marine fish are not clear. Embryo (3-5 hpf) and newly hatched larvae of marine medaka (Oryzias melastigma) were exposed to 0.01-1.28 mg L^-1 waterborne Cu to investigate the developmental toxic effects. The results showed that Cu accumulation in the whole embryos presented a dose- and time-response increase while it decreased dramatically once hatching. Most of Cu accumulated in the chorion suggests that chorion is an effective barrier to Cu absorption. However, Cu that penetrated chorion and entered embryo still caused significant lethal and sublethal effects. Cu concentrations at ≥0.16 mg L^-1 led to low hatchability, delayed hatching, high mortality, morphological abnormalities and increased egg size in the embryos. Heart beats and the total body length of the newly hatched larvae were significantly increased when exposed to ≥0.02 mg L^-1. Cu exposure accelerated early development and promoted or delayed hatching of embryo. High Cu concentration (≥0.16 mg L^-1) exposure induced morphological abnormalities of embryo and larvae, particularly skeletal and vascular system abnormalities and reduction of pigmentation. The 30 d-LC₅₀ for embryo development was 0.138 mg L^-1 and 7d LC₅₀ for larvae survival was 10.15 mg L^-1, demonstrating that embryos were more sensitive to Cu than larvae. In summary, O. melastigma embryos development is highly sensitive to Cu exposure, and the sublethal effects occurred at low Cu concentration might be as potential biomarkers in marine fish.