Chapter 15 The biology and toxicology of retinoids in fish

Publisher This chapter summarizes the available information about the retinoid system in fish and highlights the components that set it apart from the mammalian system. The chapter reviews the pollutant effects of toxicant exposure on the fish retinoid system, as documented in both the field and lab studies. The retinoids originate from carotenoids obtained from the diet as vitamins and are best known as visual pigments involved in signal transduction in the retina. Retinoids such as retinoic acid have been shown regulating gene expression, through binding to nuclear receptors, thereby controlling aspects of growth, reproduction, and development. The chapter explains the structure and metabolism of retinoid and retinoic acid action and signaling. Retinoids are lipophilic, polyisoprenoids with a cyclohexane ring and refers to a broad grouping of compounds from animal sources including retinol, retinal and retinoic acid (RA), as well as synthetic forms developed for pharmaceutical purposes. In mammals, RA is involved in a diverse array of biological processes including cell growth, differentiation and death, embryonic development, and reproduction. There is growing evidence that toxicants can disrupt the retinoid system in fish. The most commonly reported response is a reduction of hepatic retinoid stores, which is emerging as a sensitive marker of organic pollutant exposures.