Physiology of Finfish and Shellfish (2+1)

5.2.22. Pheromones

Pheromones are a type of hormone that are mainly for the purpose of attracting others. About 50 years ago, Karlson and Lu¨scher coined the term ‘pheromone’ to describe chemicals that are ‘excreted to the outside by an individual and received by a second individual of the same species in which they release a specific reaction.’ Pheromones are chemical substances secreted by animals in small quantity and cause various kinds of intraspecific response. In fish, pheromones are released into the surrounding water and the information is quickly picked up by other individuals of the species causing in their behaviour. Only minute quantities of pheromones are released into water and this helps in

1. Recognition of species and sex.
2. Recognition of territory
3. Warning and social behaviour

Pheromones play an important role in the recognition of species and sex. Experiments have shown that males of some species like Ictalurus and Brachydanio renio are attracted by the odour of the female. In some species odour of the ripe female attracts the male, while in others odour of the mature male fish attracts the female. These chemicals or attractants are produced by the gonads and are released into the water directly or through urine.

Recognition of territory is also an important function of pheromones. Many species of fish are capable of conditioning the surrounding water by releasing pheromones and this is recognised by other members of the species. It has been suggested that the homing behaviour of migratory species is influenced by pheromones. Thus, the adults of Atlantic salmon, Salmo salar return to the same river and reach the same area by recognising the odour left by young fish.

Pheromones produced by special club cells of the epidermis of the skin produce alarm reaction. Thus, when a predator catches and eats a fish, the club cells are broken and release the pheromone. This information is immediately picked up by the olfactory organs of other individuals of the group, who scatter and escape from the enemy. The chemical nature of these pheromones is not definitely known and these may be amino-sugars. Besides the alarm or fright reaction, the pheromones may influence other behaviour of the fish such as schooling. The alarm substance may not be secreted by all the species, but it is apparent that the pheromones play an important role in guiding the behaviour of the fish.