However, subtle changes to their body chemistry caused by space flight may place them at greater risk if they undergo medical treatment back on Earth.

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Its full metal body, enriched by subtle wavy patterns, conveys a sense of timeless elegance.

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Careful study, however, found subtle differences in the Arowana's body shape by gender.

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"It's not something subtle here, it's a major effect on the way the retina develops that requires light going through the body, " said Prof Richard Lang, from Cincinnati Children's Hospital.

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