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

Abstract

Olfactory cues play an important role in the behavior of fishes, such as the procurement of food, recognition of sex, defense against predators, parental behavior, and orientation. By monitoring and three-dimensional photographic techniques, analyses were made of some aspects of orientation mechanisms through olfaction. None of the marine and freshwater species investigated moved randomly in an experimental environment void of directional cues. When changing direction, the radius of the curve is fixed within fairly narrow limits and seems to be species-specific. Left and right-hand turns are not evenly distributed. This locomotor behavior results in a non-random pattern of relatively rigid parameters. The introduction of an odor without directional cues causes these parameters to change drastically. Invariably, the radius of the curve in changing direction decreases and the ratio of left-handed to right-handed turns is greatly changed in most experiments. When an attractant odor is introduced uni-directionally, none of the species studied could locate the source, unless the odor was associated with a differential in the rate of flow of the water. It is suggested that an attractant odor releases rheotactic response, which was not present in the animal in the experiments previously referred to, so that the localization of the source of the odor takes place through rheotaxis rather than through orienting cues provided by the odor gradient. Furthermore, it is proposed that this mechanism forms the basis for homing orientation in those migrating species in which olfactory cues are required for the localization of spawning grounds in river systems.