An artificial fertilization method with the Japanese medaka: Implications in early life stage bioassays and solvent toxicity

An in vitro fertilization method was used to study the effects on medaka (Oryzias latipes) embryos reared either from 0.5 h (early blastodisc) or 6.5 h (early blastula) post-fertilization for 200 h in varying concentrations of dimethyl sulfoxide (DMSO), methanol, or ethanol (0.06, 0.13, 0.25, 0.50, 1.00, 1.50, and 2.00% v/v). Physiological and anatomical parameters in embryos and larvae were examined and compared across groups. Among the three solvents, ethanol induced the most severe effects in embryos and larvae. Based on anatomical abnormalities, no differences were observed between both windows of exposure to DMSO. Similarly, no differences were observed at concentrations of methanol or ethanol ⩽0.25% v/v. Only two endpoints, hatching success for methanol (EC50 1.84% v/v), and spinal deformities in larvae for ethanol (EC50 0.60% v/v) pointed the earlier window of exposure as significantly more sensitive. Further research is needed to investigate if using this exposure methodology for chemicals with more specific modes of action may result in increased sensitivities.