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surveys of olfactory epithelium of recovered fish detected <br />ciliated olfactory receptor cells. <br />Other Toxicant Effects <br />During toxicant exposures, there were indications that <br />copper and zinc concentrations were adversely affecting behavior <br />and survival of test organisms. Approximately l00 of Colorado <br />squawfish in the highest 24- and 96-h copper concentrations (266 <br />and 66.5 µg/L, respectively), and highest 96-h zinc concentration <br />(1492 µg/L) suffered partial or complete loss of equilibrium, or <br />died as a result of toxicant exposure. <br />Scanning Electron Microscopy <br />For each toxicant and duration of exposure, systematic SEM <br />surveys always detected one or more ciliated receptor cells in <br />control fish. Surveys also detected ciliated receptor cells in <br />fish from the 96-h 1492 µg/L zinc exposure, but they failed to <br />detect receptor cells in fish from other copper or zinc <br />treatments. Microvillous receptor cells were detected only <br />occasionally in control fish and their presence or absence in <br />toxicant-exposed fish was not considered to be a reliable measure <br />of adverse effect. <br />Surveys of olfactory epithelium were complicated by small <br />size and early developmental state of olfactory rosettes. In <br />addition, profuse ciliated epithelial cells interfered with <br />ability to view receptor cells. However, there was no indication <br />12 <br />