Perception of Pathways by Fishes in Migration

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Abstract
Fish swimming to a feeder or breeding area orient to physical, chemical, or other biological stimuli in the environment. Orientation cannot be explained in terms of clairvoyance or extrasensory perception, and must have a physiological basis. The actual visual field of a fish is smaller than that of a land animal and small amounts of light may provide the stimulus. The sun may provide a rough compass direction much as has been demonstrated for birds and bees, although the specific mechanism has not yet been demonstrated for fish. Experiments with the minnow Phoxinus have shown that environmental features are more important in orientation than some "celestial mark" in the "heavens." Fishes also use tactile and auditory references, and may detect increases in water pressure through their neuromasts and the end-organs of their sensory lines and canals. Odor perception may be the directive cue to homing salmon and bluntnose minnows. Minnows in which the olfactory tissues were destroyed could not discriminate between 2 creeks which differed in amount of total nitrogen present. Experiments with sexually mature coho salmon, some of which had the nasal sac plugged with cotton, showed that most of the normal fish returned to the stream of their first choice, whereas fish with plugged nostrils returned in a nearly random fashion. Hydrographic reference points have also been suggested as guides. The place of contact of 2 water masses might have differences in salinity, dissolved gases, and odor, all perceptible.

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