MORPHOMETRY OF FISH INNER-EAR OTOLITHS AFTER DEVELOPMENT AT 3G HYPERGRAVITY

Size and asymmetry (size difference between the left and right sides) of inner ear otoliths of larval cichlid fish were determined after a l ong-term stay in moderate hypergravity conditions (3g; centrifuge), in the course of which the animals completed their ontogenetic developme nt from hatch to freely swimming. Neither the normal morphogenetic dev elopment nor the timely onset and gain of performance of swimming beha viour were impaired by the experimental conditions. However, both utri cular and saccular otoliths (lapilli and sagittae, respectively) were significantly smaller after hyper-g exposure compared to Ig control sp ecimens raised in parallel. The asymmetry of sagittae was significantl y increased in the experimental animals, whereas the respective asymme try of lapilli was pronouncedly decreased compared with the Ig control s. These findings suggest that growth and development of bilateral asy mmetry of otoliths are guided by the environmental gravity vector. Som e of the hyper-g animals revealed a kinetotic behaviour on transfer to normal Ig earth conditions, which was similar to the behaviour observ ed in previous experiments on the transfer from Ig to microgravity (pa rabolic aircraft flights). The lapillar asymmetry of kinetotic samples was found to be significantly higher than that of normally behaving e xperimental specimens. No differences in asymmetry of sagittae were ob tained between the two groups. This supports an earlier theoretical co ncept, according to which human static space sickness might be based o n asymmetric utricular otoliths.