Fish swim more silently with forked tails

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Fish with forked tails are more likely to be found across a range of water depths, including deeper habitats, where the shape of the tail may allow for 'stealth swimming'.

Swimming 'silently' is important in deeper water, where visibility is reduced and fish need to rely more on sensing changes in water pressure to capture prey and avoid predators.

Fish that are able to live across a range of depths have an increased chance of surviving natural disasters such as cyclones.

The international team of researchers, led by Dr Tom Bridge from the ARC Centre of Excellence for Coral Reef Studies at James Cook University found that the 'caudal fin aspect ratio', which measures the shape of the fishes tail, is the best predictor of which fish can live in a range of deep and shallow reefs.

"Fishes with more forked tails are significantly more likely to be found in both shallow and deep habitats than species with more rounded tails," Dr Bridge said. It's suspected that the forked tail allows for 'silent' swimming.

Study co-author Dr Osmar Luiz from Macquarie University says: "Identifying which species can occur over a broad depth range is important for understanding which fish are more vulnerable to local population declines and extinction, particularly from disturbances such as cyclones and coral bleaching events."

The study is published in the journal Proceedings of the Royal Society B.