The fishes are the most numerous and diverse of the vertebrate groups, stemming from a long and branched line of ancient ancestry. Though they account for more than half of the world's total vertebrate species, they have essentially retained the same anatomical plan for 450 million years (Maisey, 1996). What accounts for the stamina of these living fossils? During their evolutionary history, fishes have given rise to a vast diversity of forms, not merely to survive but …showed first 75 words of 1915 total…

…showed last 75 words of 1915 total…recognition, pheromones identify a fish and also his position in social hierarchies if one exists. In predator avoidance, epidermal cells release a fear pheromone when the skin is broken and prompts other fish of the same species in to predator evasion mode. The same pheromone also inhibits cannibalism. The ability to produce electrical signals is only possessed by a few groups, in which it serves the functions of visual and auditory signals in other fishes.