Seasonal variations of vitamins A, E and carotenoids in eelpout (Zoarces viviparus) from a Danish fjord, in relation to reproductive cycle

Abstract Retinoids (vitamin A) and tocopherols (vitamin E) are essential for key biological functions in vertebrates, including cell growth, cell death and differentiation, embryonic development, reproduction and vision. In fish, however, much less is known about the retinoid functions, although retinoic acid has been shown to be involved in embryonic development. In this study, we quantified the levels of different retinoids, carotenoids and vitamin E in various tissues of both adult and embryos of the viviparous fish eelpout ( Zoarces viviparus ). Our results demonstrate clear seasonal differences in the levels of these vitamins in the liver of the female fish as well as in its ovarian tissues, eggs and/or embryos. Overall, this study is a baseline assessment and describes the annual variations in the vitamin status by comparing the tissue distribution of retinoids, carotenoids and vitamin E. This baseline study investigates the natural background levels of these compounds and relates their seasonal fluctuations to the reproductive cycle in the viviparous eelpout. The results of this study strengthen the current evidence base necessary to understand retinoid pathways during fish development. This understanding is crucial for utilizing retinoid composition in fish as a biological response to exposure to environmental pollution with hazardous substances in the marine environment.