Fish, Shoaling Behavior, and the Role of Pheromones

Introduction Shoaling is a widely important mechanism used by fish in freshwater and marine environments. Although used rather loosely in conjunction with the term “schooling,” the two words differ in definition by nature of organization. Where shoaling refers to a congregation of conspecific fish that stay together, schooling indicates that those fish are swimming in a coordinated fashion. Shoaling is not a learned behavior, but one in which a species is born to participate. This conduct evolved in as many as 50% of all fish species for a number of reasons. The incentives for shoaling mostly stem from the simple premise that all animals have three jobs in life: eat, reproduce, and avoid being eaten. From this, we can derive the motives for shoaling behavior. To facilitate these life goals, natural selection has chosen for shoaling behavior to increase foraging success, reproductive convenience, hydrodynamic efficiency, social interaction, and predator avoidance (Moyle and Cech 2003, Brahams and Colgan 1985). Fish that engage in shoaling have developed several methods for facilitating the interaction with others. Individually, shoaling fish have eyes on the sides of their head to better see others in the shoal. Furthermore, it has been demonstrated that vision is important to cohesion because of the inability of most species to maintain schools at night, rather just shoals (Shaw 1961). “Schooling marks” such as prominent stripes or spots help fish recognize others as members of their own species. As a mechanoreceptor, the lateral line system is present in all shoaling fish, assisting in the detection of proximity and movement of other individuals in the shoal. Aside from physiologically based communication adaptations, chemical communication in the aquatic environment plays a large role in fish interaction. There is ample evidence that chemical composition, concentration, flux, and hydrodynamic transport all have profound effects on chemically mediated

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