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Last Updated: Friday, 4 May 2007, 15:14 GMT 16:14 UK
Tags follow 'Nemo' fish to home
An adult orange clownfish (Science and S.R. Thorrold)
About 60% of the young orange clownfish found their way home

The remarkable homing instincts of some coral reef fish have been revealed.

A team tagged two species of reef fish larvae to see where the juveniles were going after spending weeks and even months maturing in open sea.

It found most of the orange clownfish - made famous by the Finding Nemo movie - and vagabond butterflyfish returned to the reef where they had first hatched.

Writing in the journal Science, the team said the discovery could have implications for marine protection.

"Marine fish lay very small eggs, and when they do, they are released into the water column," explained co-author Professor Geoff Jones from James Cook University in Queensland, Australia.

"They develop into a really tiny little larvae that we think drift around in the water currents, sometimes for months.

"The missing link in our understanding of coral reef fish has always been: where do the larvae go?"

Help from Mum

But until now, finding this out has been extremely tricky - attaching tags to miniscule larvae is not an easy task.

So the international team of researchers tackled the problem by getting the mother to help.

Satellite image of the Kimbe Island  (Science)
The study took place on a small reef in Kimbe Bay
They did this by collecting female coral reef fish from a small 0.3 sq km reef in Kimbe Bay, Papua New Guinea, and injecting them with a rare, stable barium isotope.

The females pass this isotope to their developing offspring where it accumulates in their bones, giving the baby fish unique chemical signatures.

A few weeks later, the team returned to the reef and collected young fish to test them to see if they carried the "tag".

"We found that 60% - well over half - were coming back to the small island reserve, which was an unexpected result," Professor Jones told the BBC.

Navigational feat

The scientists are uncertain how the vividly coloured orange clownfish and vagabond butterflyfish perform this feat but hope to find out with further research.

An adult butterflyfish (Science and R. Patzner)
"Perhaps they are somehow remaining in sensory contact with their home island and are able to maintain their position and not end up drifting too far away," said Professor Jones.

"Or maybe they are getting carried away, but they have a homing mechanism to swim back to their home reef."

Although the study was carried out on two species, Professor Jones believes the finding may apply to other coral reef fish too, and if this is the case, it could have consequences for marine conservation.

It shows that small no-take marine reserves are a good way to protect over-fished species, he said, because there should be enough juveniles returning to the area to sustain numbers over time.

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