Functional asymmetry estimated by measurements of otolith in fish.

It is widely accepted that the incidence of space adaptation syndrome (SAS) is due to a mismatch of sensory information from various receptors to the central nervous system. We investigated the functional asymmetry of vestibular organ, which may caused sensory conflict in space, by measuring the weight difference of otolith between left and right side in goldfish and carp. In the goldfish utricular otolith, the maximum difference was 0.8 mg and the mean difference was 0.091 mg. The percentage of weight difference to the heavier otolith was calculated. The maximum difference was 20.57% and the mean was 3.035%. A difference exceeding 10% was found in only 2 goldfish. In the carp utricular otolith, the maximum percentage difference of weight was 24.8% and the mean was 3.491%. A difference exceeding 10% was found in only 3 carp. The maximum difference of saccular otolith was 11.8% with the mean of 6.92%, and that of lagenar otolith was 32% with the mean of 5.6% in goldfish. The close relationship of utricular otolith weight between both sides suggested that the otolith asymmetry might not be the main factor inducing SAS at least in goldfish and carp.