Chemical Perception of Food: Chemical perception of food in fishes was first clearly demonstrated experimentally at the turn of the last century in elasmobranchsand in many teleosts.

Aquarium held Smooth-hound, Musteluscanis, were shown to be unable to recognize the presence of food substances when their nareswere pluggedwith cotton; food recognition was regained when the cotton was removed.


Since then the use of chemoreceptionin the foraging and directed movements of fishes has been demonstrated on numerous occasions.

Pathways of an aquarium-held eel (Anguilla anguilla) in search of an odor(phenyl-ethyl alcohol) to which it has been conditioned. A wad of cotton soaked in the odorous

solution was placed in the hollow tube. In the experiment on the left, localization of the source of the odorrequired 1 minute (straight-line distance 25 cm); in the experiment on the right, 4 minutes were required (distance 35cm).

Pathways of an aquarium-held eel (Anguilla anguilla) following a trail of phenyl-ethyl alcohol, laid down by means of a pipette, leading to the source of the odor in the

hollow tube. In the experiment on the left, localization of the source of the

odorrequired 2 minutes; in the experiment on the right, 4 minutes were required (distance 35 cm).



Reproductive Behavior: Chemoreception is known to play a role in courtship, parentalcare, and aggressive behavior in breeding fishes.

One of the clearest examples of the role of chemoreceptionin parental care comes from work on the cichlidHemichromisbimaculatus(often called the jewel fish).


A pair of cichlids was allowed to spawnin one of four

clay flowerpots. After spawning or hatching, the pot containing the eggs and frywas removed and another put in its place. The pot with the developing embryos was placed randomlyin one of four cylinders from which water was supplied to the tanks (through the clay pots in the tank). Once the eggs were hatched, the parentsalways gathered around the pot that came from the cylinder containing their young.


Furthermore, they displayed parental behaviortypical of the species even though no young were visually present. The response lasted the full three weeks

typical of the period of their parental behavior. When the late stage young were replaced with newly hatched embryos, the female parent switched her behavior to

that appropriate for newly hatched young, continually fanningthe pot and the imaginary embryos with her pectoral fins to keep oxygenlevels high.


Migration: Olfactionhas been shown to play key roles in the migration of salmonidsand freshwater eels (Anguillidae). In the former case, the specific odors are imprintedon the young during development and early rearing.


The American (Anguilla rostrata) and European (Anguilla anguilla) freshwater eels spawn in the Sargasso Sea—the elvers(metamorphic stage just before entry into freshwater) use olfaction to migrate from the sea to freshwater. They show positiverheotaxisto freshwater but not to seawater.

However, in this case, unlike salmon, the specific odors of freshwater are notlearnedat some earlier life-history stage, because the full-grown parents of these elversmigrate from freshwater to the Sargasso Sea to spawn and subsequently die.


Predator Avoidance: One of the best examples of the role that olfaction can play in predator avoidanceis the Schreckstoffor alarm substancesecreted by specialized epithelial cells of ostariophysanand various other fishes. This is an example of predator avoidancethrough the recognition of injury to conspecific or closely related species.

In addition, there are numerous examples of prey recognitionof the odorof potential predators. Such recognition may be learned or innate (inherited). One of the best examples of what appears to be innate avoidance behavioris seen in the response of Pacific salmon(genus Oncorhynchus) to various substances.

Pacific salmonmigrating upstream to spawn stop their upstream movement, reverse their direction, and otherwise show an avoidanceor fright behaviorwhen extracts of various mammalian skinsare placed in the water upstream. Fifty-four other groups of substances tested gave negative results.

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