Search

Herbicides are used to control weeds and are usually targeted to processes and target sites that are specific to plants. As a result, most herbicides are not acutely toxic to fish. Exceptions to this general rule are uncouplers of oxidative phosphorylation and some herbicides that interfere with cell division. Chronic and sublethal effects have been studied for some herbicides, but fewer data are available for these effects than for acute effects. The sublethal effects of herbicides that have been studied include reproduction, stress, olfaction, and behavior. Although some of these responses have been observed in fish exposed to herbicides, these have either been observed at large concentrations that would be rarely found in surface waters inhabited by fish or, as in the case of behavior and olfaction, have not been linked to ecologically relevant responses on survival, growth, development, and reproduction. As with all pesticides, herbicides may have indirect effects in fish. These effects are mediated by herbicide-induced changes in food webs or in the physical environment. Indirect effects can only occur if direct effects occur first and would be mediated by the killing of plants by herbicides. Although this indirect effect might occur when plants are controlled by direct treatment of surface waters, indirect effects appear to be unlikely to result from use of herbicides in terrestrial systems as runoff concentrations in surface waters are, for the most part, very much less than those that could directly affect plants.

Publisher Summary This chapter discusses the neuroendocrine pathways that regulate the synthesis and release of the pituitary gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), in teleost fish with a primary focus on the multiple forms of both gonadotropinreleasing hormone (GnRH) and its receptors in relation to their actions within the brain and pituitary. Recent studies have demonstrated that a vast number of neurotransmitters, neuropeptides and other factors exert inhibitory and/or stimulatory control over the GnRH–FSH/LH system. The identity and roles of these factors at the various stages of gonadal development are also discussed in the chapter together with an examination of the manner in which the actions of sex steroids and the inhibitory neurotransmitter dopamine coordinate the activation of the GnRH–FSH/LH system during puberty and in relation to sexual maturation and spawning. Gonadal steroids and changes in steroid feedback regulation appear to play a role in mediating the seasonal/maturational differences in the availability of LH and FSH for release.

Publisher Summary 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.

Publisher Summary This chapter reviews the recent developments in the molecular and biochemical studies of metazoan cell death and summarizes recent applications of this new information to the studies of toxicology in fishes. Cell death (apoptosis) plays an important role in the development and function of tissues and organs in all multicellular organisms, including fishes. Cell death can be induced by specific developmental cues that promote active, targeted cell removal (programmed cell death) or can be the passive consequence of pathological or toxicological cell injury (accidental cell death). The chapter explains apoptosis, apoptosis as a cellular response to toxicant exposure, and cell-death detection. Apoptosis is an active, gene-directed program of cell death that results in the deliberate self-destruction and orderly removal of individual cells from a tissue. This suicidal pathway to cell death plays an instrumental role in many biological processes, including tissue morphogenesis and homeostasis, nervous system development, immune system function, and germ-cell selection. There is abundant and accumulating evidence to suggest that apoptosis may be a biologically significant response to toxicant exposure. The apoptotic removal of cells whose function has been compromised by toxicant exposure is one means by which an organism can minimize the deleterious effects of toxicant exposure. A variety of approaches are routinely used to qualitatively or quantitatively assess toxicant-induced cell death in vitro .

Publisher Summary This chapter provides an overview of gonadotropin receptor studies in fishan introduction to gonadotropin receptor studies in fish. This discussion is based on the premise that a working knowledge of receptor theory is essential to an understanding of reproductive endocrinology in fish. Although current knowledge pertaining to receptors is largely a consequence of mammalian studies, no attempt is made to provide a detailed list of their properties. The discussion focuses on the techniques used to identify gonadotropin receptors and the operational features that a hormone-binding site must possess to function as a receptor. Considerable emphasis is given to the technical aspects of receptor-binding studies performed by direct binding of hormone to gonadal tissue incubated in vitro. A final comment is made on the application of receptor-binding techniques to studies of fish gonadotropins.