Fish In Space Help Study Balance Disorders

January 31, 2008

Release from: The Hindu (India)

Twenty-six baby fish are now orbiting Earth aboard an unmanned Russian spacecraft, in a long-delayed experiment that researchers hope will lead to a better understanding of inner-ear balance mechanisms in humans.

The cichlid fish (Oreochromis mossambicus) blasted off recently from Baikonur Cosmodrome in Kazakhstan, in a Foton-M3 craft atop a Soyuz-U rocket, as part of a package of life and physical science experiments organised by the European Space Agency.

Microgravity conditions

Reinhard Hilbig and Ralf Anken, neuro- and developmental biologists at the University of Hohenheim in Germany, will monitor the larval fish to watch the growth of their otoliths — sensory organs that have a role in hearing and balance — in microgravity conditions.

Otoliths, also found in the inner ear of humans, are sensitive to gravity and linear acceleration and are essential for maintaining proper balance. They are composed of a mix of gelatinous material and calcium carbonate, which shift around in a viscous fluid when the head moves, stimulating hair cells and conveying information about movement to the brain. Scientists think a malfunctioning otolith is the culprit for conditions such as Meniere’s disease, which causes vertigo and ‘ringing in the ears’ in sufferers.

But they do not yet understand exactly how this organ works. The otoliths of fish provide a good candidate for study, says Hilbig, because they function in exactly the same way as human ones but are considerably larger. This is because fish must orient themselves underwater, where other motion clues are suppressed.

Previous tests have shown that larval fish exposed to ‘hypergravity’ conditions in a centrifuge grow smaller-than-normal otoliths than controls.

This implies that otolith development is, at least in part, under neural control, says Anken. Somehow the fish brain signals the otolith to grow smaller, as it does not need to be as big or as sensitive in hypergravity as it would in normal conditions.

The next step to confirm neural control is to test whether microgravity makes developing otoliths grow to be larger (and so more sensitive) than normal. Anken says they are expecting the otoliths to “grow uncontrollably and asymmetrically” in low gravity if under neural control.