Chemical Defense in Fishes

Chemical defense is a protective measure employed by living organisms to evade predation or infection, by the use of chemical substances which affect the physiology of potential predators. These substances may be classified into two categories. Toxins associated with mechanical devices that are injected directly into the body of enemies constitute one category and are usually called venoms. The other category comprises those that reach sensory organs of enemies through environmental media. This chapter covers only substances of the latter category which play roles in the defense of fishes, since little is known about chemistry of fish venoms except that they are all proteins as far as is known to-date. While chemical defense occurs only sporadically in vertebrates, little phylogenetic relation is found among the fishes using chemical defense and their defense substances are therefore fairly diverse in terms of their chemical structures.