Effects of Embryonic Exposure to Ethanol on Zebrafish Survival, Growth Pattern, Locomotor Activity and Retinal Development

Alcohol intake can cause a wide range of visual system abnormalities. In this study, we characterized how ethanol affects the growth, external morphology and locomotion of zebrafish, particularly with regard to retinal development. Zebrafish embryos were divided into 5 groups and put into hatching liquid for 6 hours. The embryos from 4 groups were treated with varying concentrations of ethanol (0.5%, 1.5%, 2.5% and 3% by volume) from 6 to 24 hours post-fertilization. The toxic effects of ethanol on embryonic development were assessed by mortality, hatching rate and morphologic deformity. The effects of ethanol on locomotive activity were assessed by autonomous motion detection and swimming behavior analysis. The effects of ethanol on retinal morphology were assessed by histologic, immunohistochemical and electron microscopy analyses. Ethanol treatment increased the mortality and induced growth retardation in zebrafish larvae. The locomotive activities of zebrafish embryos/larvae were impeded by exposure to higher (1.5% and 2.5%) concentrations of ethanol. Embryos exposed to higher levels of ethanol at the early developmental stage had a reduction in eye size. The ethanol treatment disrupts the architecture of the retina and reduces retinal size. Embryos exposed to 2.5% concentration of ethanol had morphologic abnormalities of the photoreceptors. Ethanol exposure also inhibited retinal cell differentiation and proliferation, but did not affect apical epithelial polarity. These findings suggest that ethanol affects the growth and external morphology of zebrafish, and higher levels of ethanol exposure can cause defects of locomotor activity and photoreceptor development.