Small Fish Models for Identifying and Assessing the Effects of Endocrine-disrupting Chemicals

Abstract

Endocrine-disrupting chemicals (EDCs), particularly those that affect the hypothalamic-pituitary-gonadal (HPG) axis of vertebrates, have become a focus of regulatory screening and testing throughout the world. Small fish species, principally the fathead minnow (Pimephales promelas), Japanese medaka (Oryzias latipes), and zebrafish (Danio rerio), are used as model organisms for several of these testing programs. Fish are appropriate models for testing EDCs, not only from the perspective of existing ecological impacts, but also in terms of species extrapolation. Specifically, there is a significant degree of conservation of basic aspects of the HPG axis across vertebrates, which provides a technically robust basis for using results from fish tests to predict likely modes/mechanisms of action of potential EDCs in other vertebrates. Different experimental designs/endpoints for partial-and full-life cycle tests with fish that enable a consideration of a broad range of EDCs are described. Examples of results with specific chemicals in tests with the fathead minnow, medaka, and zebrafish are presented and discussed in terms of sensitivity and specificity for different classes of EDCs.

Estrogenic activity of tropical fish food can alter baseline vitellogenin concentrations in male fathead minnow (Pimephales promelas)

“…Under normal circumstances, VTG levels in male fish are either undetectable or low (approximately 10,000 to 100,000 times lower than typical female concentrations [4,5]). However, when male fish are exposed to oestrogenic substances, they are capable of producing a large amount of VTG and blood concentrations can reach values similar to those in females.…”

Histopathological changes in the reproductive system (ovaries and testes) of Oreochromis mossambicus following exposure to DDT

“…Sub-lethal exposure to persistent organic compounds may alter key enzymatic activities and potentially cause reproductive effects, by reducing fecundity and population recruitment (Patyna et al, 1999). The hypothalamic-pituitary-gonadal (HPG) axis of teleost fishes, whose principal components are the hypothalamus and pituitary gland in the brain, the gonads and the liver, is generally similar to that of other oviparous vertebrates (Ankely and Johnson, 2004). The gonads are the primary organs of reproduction and, as such, will reflect substantive disturbances to the HPG axis (USEPA, 2006).…”

Use of Immunofluorescence with Frozen Sections for the Detection of Vitellogenin Year-2 Class Natural Population Rainbow Trout-A Preliminary Investigation

“…A more detailed description of the pathway and its regulation can be found in Arcand-Hoy & Benson [1]. Although both sexes preserve the ability to produce the protein VTG, it is not normally present at significant levels in the blood or gonads of male fish during their life cycle [3]. However, males cannot dispose of VTG readily, thus levels can remain high in blood plasma of males longer than in females [3].…”