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concentration ranges to levels expected to reduce survival and growth of razorback sucker. The <br />new data will be combined with data in this report to provide a description of effects over a broad <br />range of environmental and tissue concentrations. Resulting descriptive relationships will be <br />evaluated using data from the other ongoing study entitled "Selenium effects on larval razorback <br />sucker: field verification of laboratory results". This study will provide data that can be used to <br />compare predicted and observed toxicity of water collected from potential razorback sucker <br />nursery habitats along the Colorado River. <br />A shortcoming of this investigation was that bioaccumulation in the experimental food <br />chain was lower than expected. The experimental food chain was based on a design presented by <br />Dobbs et al. (1996) and used identical species of algae, rotifer, and type of selenium. The time <br />required for exchange of algae growth media (turnover rate) in the system described by <br />Dobbs et al. was 2 days. In our investigation, we attempted to maximize bioaccumulation by <br />increasing residence time of algae and growth media using a longer exchange time of <br />approximately 10 days. The slower exchange rate may have reduced bioavailability of selenium <br />in cultures as a result of sedimentation. Selenium may have been retained in dead algae that <br />accumulated over time on the bottom of culture vessels. Thus, dissolved selenium may not have <br />been available for incorporation into living algae, rotifers and fish. In future investigations, <br />exchange rate will be increased to approximately once every 3 days. This change combined with <br />a broader range of exposure concentrations should produce dietary exposure concentrations that <br />exceed predicted thresholds for toxic effects in fish. <br />25 <br />