Funding Program: Contaminant Biology

Statement of Problem: The most sensitive portion of a fish's life to the toxic effets of chemical contaminants is from embryonic development through the fry stages. This has been demonstrated to be true for numerous classes of chemicals. However, there are two shrotcomings of the standard protocols for testisng the toxicity of chemicals to early life stages of fish. First, the current tests to determine the toxicity of chemicals to early life stages of fishes rely upon waterborne exposure. This is fine for hydrophilic chemicals, but many of the chemicals that are of concern in the aquatic environment are hydrophobic and persistent. In the case of the hydrophobic compounds, the major route of exposure to the developoing fish embryo is from the chemical received from maternal deposition into the oocyte during maturation in the adult fish. Therefore, test methods are required that will allow the study of effects on hydrophobic chemicals on early life stages of fish. We have developed fish egg injection techniques at the CERC to mimic the deposition of hydrophobic chemicals into fish eggs. These techniques have been perfected for the rainbow trout, medaka, zebrafish, and bass species. The method allows for the study of other fish species that have much smaller egg sizes, such as fathead minnows or other species ofinterest. Therefore, limitations of maternal exposure are avoided and species of fishes that cannot routinely be maintained in fish culture, such as the endangered species, may be evaluated for their susceptibility to contaminants. the second shrotcoming of current test methods to study early life stage toxicity in fish is taht there are no mechanistic models that have bee developed to understand and study this type of toxicity on fish development. Such models are needed to understand various modes of action of chemicals and to be able to predict oranismal and population level effects. The modelsmust consist of endpoints of toxicity from multiple levels of organization (biochemical, cellular, organ, and organismal) in order for them to be predictive.

Objectives:  The overall goal of this project is to develop and apply innovative technology to assist in assessment of stressor levels to trust resources and their surrogates. This goal will be accomplished through the following specific objectives. 1) Characterize egg injection tec hniques for fish species with small eggs that are of interest to resource managers (i.e., threatened or endangered species) and those fish that are important in the study of fish developmental biology (e.g., medaka or zebrafish). 2) Develop biochemical, molecular and histological probes that can be used to study fish development and the effects of enviornmental contaminants. 3) Develop techniques for the study of complex mixtures of contaminants as they exist in the environment and their effects on fish development.