Detection and Discrimination of Odors of Aquatic Plants by the Bluntnose Minnow (Hyborhynchus notatus)

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Abstract
Blinded bluntnose minnows (Hy. notatus. in groups of 6 and 8, were able to discriminate, after a 2.5-month period of training, between the odors of Myrio-phvllum exalbescens and Ceratophvllum demersum when food was the reward and electric shock was the punishment. Reverse training substantiated this. Similarly, they were trained to discriminate odors of other sets of plants (I) Ranunculus tricophvllus and Anacharis canadensis; (II) Utricularia vulgaris var. americana and Vallisneria americana: (III) Potamogeton zosteriformis and p. crispus: (IV) P. amplifolius and P. vaginatus. Rinses containing odors of other plants were introduced into aquaria of fishes thus trained, in a Latin-square design by a generalization test. Of 12 sp. tested, the odors of only 2 seemed to resemble each other, i.e., when C. demersum had negative significance, the fish associated with it the odor of A. canadensis. When minnows were fatigued to a strong rinse of one species, they still detected odors of other spp. as they were superimposed. Trained minnows whose olfactory epithelium had been destroyed by heat cautery were unable to respond to plant rinses, indicating that the rinses contained a stimulating scent detected by sense of smell. Minnows could detect a water rinse of a sprig of aquatic plant diluted 1:10,000 after it had been further diluted by streaming it into a 7-gal aquarium. This demonstrates a very high degree of sensitivity. The authors postulate that these aquatic plants might well play an important role in the life of a fish as signposts to guide fish into feeding grounds, since many fishes commonly feed in turbid water, at dusk, at dawn and at night when visibility is poor. Odors of aquatic plants may also serve as attactants to immature fishes to prevent them from straying from cover, and other natural odors may direct migratory fishes in locating their homing areas.