BEHAVIORAL REACTIONS FOR THE ASSESSMENT OF STRESS IN FISHES

Behavioral reactions of fishes are measureable, adaptive features which contribute to their evolutionary fitness and, hence, can serve as biomarkers of stress. For a behavior to serve as an efficacious biomarker, it should be important to an individual's survival, growth and/or reproduction, be relatively stable under control conditions, and have a "concentration-effect" relationship with the stressor. This review summarizes the influence of numerous environmental stimuli on seven different behaviors in fishes. Avoidance-attractance behavior does not assess for stress, but rather allows a fish to avoia stressful chemicals. Of the 75 chemicals surveyed, about 1/3 are avoided at threshold concentrations that should mitigate harm, while approximately 2/3 were either not actively avoided or produced inconsistent results. Temperature selection behavior meets several criteria of a good indicator of stress. Several stimuli produced significant changes in selected/avoidance temperatures of various fishes. While only a few stimuli caused an increase, several resulted in a decrease in selected temperatures. Although conditioned learning appears to be a sensitive measure of environmentally induced stress, few studies have been published, and direct field validations are not possible. A variety of stimuli can disrupt the components of feeding, often in the parts per billion range of concentrations. Predator-prey interactions are sensitive to a variety of stressors. In trials where only prey were exposed to a potential stressor, 94% of the stressors caused an increase in prey vulnerability, usually at levels less than 96-hour LC50S. Neither of the other social behaviors reviewed, intraspecific and reproductive, although promising, has received large research attention. Studies featuring several different methods demonstrate that there is no single best behavioral bioassay method. However, depending upon the expected effects and possible mode of action, there probably is a "best" behavioral bioassay to illustrate the effects of each potential stressor.