Developmental exposures to ethanol or dimethylsulfoxide at low concentrations alter locomotor activity in larval zebrafish: implications for behavioral toxicity bioassays.

Ethanol and dimethylsulfoxide (DMSO) are commonly used as carrier solvents for lipophilic chemicals in aquatic toxicity bioassays. However, very little information has been reported on the behavioral effects of these solvents. In this study, we examined the effects of ethanol and DMSO on development and locomotor activity by a zebrafish embryo-larval bioassay. The zebrafish were exposed to different concentrations (control, 0.01, 0.1, and 1%) of ethanol or DMSO from blastula stage to 144 hour-post-fertilization (hpf). Hatchability, survival, and abnormalities were monitored every 12h, and locomotor activity of the larvae was analyzed at 144 hpf. Hatchability was not affected by the ethanol or DMSO treatments. No effect on survival was observed except the 1% ethanol group suffered 89% mortality during 108-120 hpf. No developmental defects were observed in any of the solvents at the 0.01 and 0.1% concentrations, but significantly higher deformity rates occurred with 1% ethanol and DMSO groups. Hyperactivity and less tortuous swimming paths were observed in all ethanol and DMSO concentrations. Based on this study, we suggest that data of behavioral toxicity bioassays using ethanol or DMSO as carrier solvents should be interpreted cautiously, because the solvents at low concentrations could alter locomotor activity of larval zebrafish without causing any observable developmental defects.