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chemosensory pathway by which fright pheromone is detected <br />(Hara 1971). <br />Behavioral assays were initiated immediately after <br />conclusion of the toxicant exposure period. Fish from each <br />replicate were randomized to flow-through observation aquaria <br />suitable for video recording. Observation aquaria were <br />1OX20X15-cm high, and depth of water was 12 cm. The back and <br />sides of aquaria were shielded with black poster board to <br />visually isolate fish and increase contrast for video recording. <br />Twenty aquaria were arranged on a rack and the entire apparatus <br />was enclosed with black poster board to reduce effects from human <br />disturbance. Ports opposite each aquarium allowed access for the <br />video camera lens. <br />Fright-pheromone extract was prepared by removing epidermis <br />from donor Colorado squawfish, starting just posterior to the <br />head and extending back to the anterior insertion of the caudal <br />fin. Epidermis was cut into pieces, homogenized (Omni-mixer, <br />Ivan Sorvall, Inc., Norwalk, Conn.), and diluted to 12.5 g/L <br />epidermis in dilution water. Aliquots (0.1 ml) of <br />fright-pheromone extract were introduced into observation aquaria <br />through injection ports in the water-delivery system and final <br />concentration of the extract was 0.625 mg/L epidermis. Injection <br />ports were located outside of the enclosed apparatus. A <br />continuous flow of dilution water from a head box to aquaria <br />mixed fright pheromone after its introduction. Dye studies <br />showed that homogeneous mixing occurred in approximately 10 s. <br />6 <br />