Which sex is best for coral reef fish

Puberty blues: goby fish choose their sex to find a mate

Research on the Great Barrier Reef has revealed that some young reef fish can choose when they mature and which sex they want to be when they grow up.

Research conducted by JP Hobbs, an honours student at James Cook University, Townsville, focused on a colourful goby that lives in bushy corals. The research may win him a British Council sponsored study tour of the UK.

Announcing his research results at Fresh Science in Melbourne today, JP said, “We already know that lots of adult fish change sex. Now we’ve discovered that juvenile fish also possess this flexible sexual development,” he says. “With juvenile coral gobies this flexible sexual development is influenced by social conditions.”

JP found that juveniles only mature when they meet an adult fish. If they meet a male fish they mature as females and vice versa.

“It all relates back to a coral goby’s lifestyle,” he says. “The big adult gobies muscle their way into the larger corals where they form a breeding pair.”

“Juveniles are not allowed to live with the adults and are forced to live by themselves in corals too small to support a breeding pair. Here they eagerly await the disappearance of an adult so that they can enter the larger coral and pair up with the remaining adult.”

“With all the larger corals occupied by breeding pairs, there are very few opportunities for a juvenile to ‘get lucky’. So it makes sense for a juvenile to delay maturing until it finds a partner and then to mature into the opposite sex of the newfound adult.”

“We suspect this flexibility in juvenile sexual development also happens in many other reef fish. After hatching, fish larvae drift onto reefs and have no idea as to how many males and females are on a reef,” he explains. “Flexibility in sexual development will enable a juvenile to mature into the best sex for obtaining a mate.”

“It’s important that we understand what’s happening with these fish as there are implications for:

• conservation – the coral goby only lives in bushy corals which are very vulnerable to coral bleaching;
• aquaculture – to get the best growth rates, farmers need to understand how to stop fish from maturing;
• fisheries management – sex-changing fish require different management practices.”

JP is presenting his research to the public for the first time thanks to Fresh Science, a national program to bring public attention to the remarkable unsung achievements of young Australian scientists. He will be speaking to the public and school students about his work on Tuesday 19 and Wednesday 20 August at the Melbourne Museum.