Fish uses tool to break up food

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A scientist from Poland has recorded one of the first documented cases of a fish using a tool to aid feeding.

Dr L Pasko of the Institute of Zoology at the University of Wroclaw was observing the Hardwicke's wrasse, Thalassoma hardwicke, in an aquarium and noticed that when the fish was fed pellets that were too large to swallow or break with its jaws, it carried the pellet away to an 'anvil' to break it up into pieces small enough to be swallowed.

The behaviour was frequently repeated and observed in detail 15 times, so Pasko says it's not a one-off incident.

" nearly always successful, and remarkably consistent, suggesting that the rock selected for an anvil is remembered and its functional qualities or other factors may play a part in its choice.

"These observations agree with evidence for other advanced cognitive abilities in members of the genus Thalassoma and suggest that, for welfare demand, rocks with rough surfaces should be provided to these fish, especially when they receive hard food for variety," the author wrote.

Pasko said that there are few cases of fish using either tools or substrate anvils as pseudotools. The results of the study are due to be published in a forthcoming issue of the journal Zoo Biology.