To investigate the disruptive effects of chronic monochromatic light exposure during early visual development on spectral preference in juvenile zebrafish ( Danio rerio ), larvae at 28 days post-fertilization were randomly divided into four groups and exposed for 56 days to white light (full visible spectrum), blue light ( λ =458 nm), green light ( λ =523 nm), or red light ( λ =628 nm). After the exposure period, spectral preference behavior was assayed and retinal photoreceptor opsin gene expression was quantified. Fish exposed to a given monochromatic spectrum exhibited a significant preference for both white or red light and for the spectrum to which they had been exposed; expression of the retinal opsin gene corresponding to the exposure spectrum was also significantly up-regulated. The findings indicate that chronic monochromatic light exposure during early visual development can reshape spectral preference in juvenile zebrafish, likely by modulating the expression of retinal photoreceptor-specific opsin genes.