Defense behavior of fish against predators and parasites

This paper is a review of empirical and theoretical studies of the behavioral mechanisms and ecological consequences of the anti-predator and anti-parasite activities of teleost fishes. While the individual and cooperative behaviors used by fish to protect themselves from predators have received marked attention from researchers in the fields of ecology, ethology and applied fish biology, the behaviors by which fish protect themselves from parasites have been poorly investigated. Generally, free-swimming parasites, which are difficult to distinguish, do not elicit any marked behavioral response from fish prior to contact. We hypothesize that the behaviors by which fish avoid parasites are much more efficient for fish in groups than they are for solitary fish. Early avoidance of predators and parasites is compared with the behavioral tactics fish use when such enemies are in close proximity. Individual versus cooperative tactics, as well as the role of learning, are also analyzed. Learning is more important for behaviors which protect fish from predators than those which they use against parasites, especially at the level of individual fish. Finally, we briefly discuss the importance of coordination of anti-predator and anti-parasite activities, which present the most complicated tasks for fish and intriguing problems for researchers.