Alarm substance recognition and predator avoidance by chinook salmon (Oncorhynchus tschawytscha) following exposure to an organophosphate pesticide

Abstract

The sense of smell in fish is thought to be important for behaviors associated with alarm scent recognition and predator avoidance. Olfactory function of juvenile chinook salmon was evaluated in two separate experiments following 2-h immersion exposures to 0, 1, 10, or 100 microg diazinon/L. In the first test system, groups of 10 salmon were transferred to the prechoice zone of a Y-maze fluviarium with parallel streams of water. A dilute alarm scent composed of either chinook skin extract or L-serine was pumped into the water supply of one arm. Fish were allowed to choose either upstream arm by raising a containment screen for 10 min, then their positions were photographed and the screen lowered. In the second test system the relationship of diazinon exposure to predation susceptibility was directly examined by transferring groups of 20 salmon (10 diazinon-exposed, 10 control) to troughs containing a protective cover. These salmon were given two olfactory warnings by delivering conspecific skin extract to both their transfer container and the predation tank they entered. After a 2-min prey acclimation period, larger predator rainbow trout were allowed access to the downstream section of the tank containing the test salmon. The combined fish were observed until approximately 50% of the prey fish had been consumed. Statistical comparisons indicated that although the salmon did avoid the water streams containing alarm scents, none of the diazinon exposure levels resulted in significantly different outcomes from the controls (alpha=0.05) in either the two-choice maze study or the predation study. Possible environmental and population implications are discussed in light of related olfaction and diazinon studies.