Species-Specific Pheromones and Their Roles in Shoaling, Migration, and Reproduction: A Critical Review and Synthesis

Many fish species have evolved the ability to locate and identify conspecifics for the purposes of shoaling, migratory orientation, and reproduction. The odor of conspecifics appears to play a significant role in all of these processes, which are all species-wide (and sometimes broader). Shoaling is common to both juvenile fishes and adults; and where studied, an olfactory component has consistently been implicated along with a role for multiple compounds. In the case of the goldfish, both polar and nonpolar fractions have been isolated and described; these also appear to facilitate adult recognition in combination with hormonal products. In addition, conspecific odor has been found to play significant roles in migratory orientation in many fishes. A migratory pheromone has been partially identified in the sea lamprey and found to be a complex mixture that includes bile acid metabolites and unknown compounds. Similar data exist for some migratory salmonids for which there is evidence that sensitivity to conspecific odors is based on processes that occur early in development. In addition, dozens of sexually mature teleost fishes appear to recognize conspecifics using odors that include mixtures of relatively common hormonal products. However, the natural odor of sexually mature fish odor has only been thoroughly examined in the common carp, and unidentified polar products have been found to complement hormonal products. We hypothesize that many fish have evolved to recognize complex, species-wide mixtures of relatively common chemicals as pheromones-the composition and function of which may change with life history stage and be modified by developmental processes and experiences.