Chemical avoidance responses of fishes.

The hydrosphere is a repository for all of our waste and mistakes, be they sewage, garbage, process-affected waters, runoff, and gases. For fish living in environments receiving undesirable inputs, moving away seems an obvious way to avoid harm. While this should occur, there are numerous examples where it will not. The inability to avoid harmful environments may lead to sensory impairments that in turn limit the ability to avoid other dangers or locate benefits. For avoidance to occur, the danger must first be perceived, which may not happen if the fish is 'blinded' in some capacity. Second, the danger must be recognized for what it is, which may also not happen if the fish is cognitively confused or impaired. Third, it is possible that the fish may not be able to leave the area, or worse, learns to prefer a toxic environment. Concerning generating regulations around avoidance, there are two possibilities: that an avoidance threshold be used to set guidelines for effluent release with the intention of driving fishes away; the second is to set a contaminant concentration that would not affect the avoidance or attraction responses to other cues. With the complexities of the modern world in which we release diverse pollutants, from light to municipal effluents full of 1000s of chemicals, to the diversity present in ecosystems, it is impossible to have avoidance data on every stimulus-species combination. Nevertheless, we may be able to use existing avoidance response data to predict the likelihood of avoidance of untested stimuli. Where we cannot, this review includes a framework that can be used to direct new research. This review is intended to collate existing avoidance response data, provide a framework for making decisions in the absence of data, and suggest studies that would facilitate the prediction of risk to fish health in environments receiving intentional and unintentional human-based chemical inputs.