Domestication effects on aggressive and schooling behavior in fish

Although the behavioral consequences of domestication in fish have long been the subject of considerable interest among aquaculture geneticists, there is not yet a clear understanding of the conditions under which aggression increases or decreases during domestication. In addition, very little is known about how behaviors correlated with aggression may be altered by domestication. In this paper the evidence for an increase as well as a decrease in aggression during domestication in fish is first critically evaluated. Then the various mechanisms by which competitive behavior in fish can affect individual growth rates under natural or artificial conditions are described. It is concluded that the direction and intensity of any phenotypic change in food-related agonistic behavior following natural or artificial selection for rapid growth will depend on the relationship between agonistic behavior and access to food. Indirect selection on agonistic behavior as a result of direct selection on growth will be significant if selection is conducted under competitive conditions that promote aggressive interactions, and will be positive or negative depending on whether food is limited or available in excess. Changes in aggression induced by domestication are likely to induce changes in behaviors that are affected by aggression including schooling behavior. The tendency to school results from a balance between attracting factors and repelling factors. This balance between competitive (repelling) and antipredator (attracting) tendencies can be altered by domestication and such behavioral alterations may affect survival of wild populations if domestic stocks are allowed to interbreed with wild stocks.