DEVELOPMENT OF THE OLFACTORY SYSTEM OF THE WHITE SUCKER, CATOSTOMUS-COMMERSONI, IN RELATION TO IMPRINTING AND HOMING - A COMPARISON TO THE SALMONID MODEL

White suckers, Catostomus commersoni, use olfactory cues to return to the same spawning stream year after year. If we assume that they follo w a model similar to the well-known salmon model, olfactory imprinting must occur very early in their development. We describe the time of m igration from the nursery stream in relation to the development of the white sucker olfactory system to determine if the requisite anatomica l structures are present which would permit imprinting. At hatching th e olfactory placode is present and beginning to differentiate, the lum en of the olfactory capsule is starting to form, and the olfactory tra ct projects into the telencephalon. Larvae migrate approximately 2 wee ks later or at a size of 14 mm TL. At this time olfactory cilia are pr esent, the olfactory tract is robust and the telencephalon is beginnin g to differentiate. Therefore, it appears that the fundamental neural structures necessary for imprinting are present. A comparison with sal mon, however, clearly demonstrates that the white sucker olfactory app aratus is not as well developed as that of salmon at time of migration . This raises the question of the ability of white suckers to imprint in the same manner as salmon and whether the salmonid model is applica ble to white suckers. Alternative imprinting hypotheses are discussed.