Some Aspects of Olfaction in Fishes, with Special Reference to Orientation

Olfactory cues play an important role in the behavior of fishes,such as the procurement of food, recognition of sex, defenseagainst predators, parental behavior, and orientation. By monitoringand three-dimensional photographic techniques, analyses weremade of some aspects of orientation mechanisms through olfaction.None of the marine and freshwater species investigated movedrandomly in an experimental environment void of directionalcues. When changing direction, the radius of the curve is fixedwithin fairly narrow limits and seems to be species-specific.Left and right-hand turns are not evenly distributed. This locomotorbehavior results in a non-random pattern of relatively rigidparameters. The introduction of an odor without directionalcues causes these parameters to change drastically. Invariably,the radius of the curve in changing direction decreases andthe ratio of left-handed to right-handed turns is greatly changedin most experiments. When an attractant odor is introduced uni-directionally,none of the species studied could locate the source, unlessthe odor was associated with a differential in the rate of flowof the water. It is suggested that an attractant odor releasesrheotactic response, which was not present in the animal inthe experiments previously referred to, so that the localizationof the source of the odor takes place through rheotaxis ratherthan through orienting cues provided by the odor gradient. Furthermore,it is proposed that this mechanism forms the basis for homingorientation in those migrating species in which olfactory cuesare required for the localization of spawning grounds in riversystems.