Why do fish float when they die? © Getty Images

Why do fish float when they die?

Most fish sink to the bottom of their habitats when they die but they become more buoyant as the process of decomposition takes over.

Asked by: Niall Woodbury, Bury

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Most fish are slightly denser than water, so sink immediately after death. However, like a drowned human, they become more buoyant over time as bacterial decomposition produces gases inside the body. Usually, enough gas builds up in body cavities to make the corpse float, like an inflated balloon. That’s not always so, as I can testify from my own fish tank: they occasionally just decompose unnoticed on the bottom.


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