Secrets of a sex-changing fish revealed

JULY 10, 2019

by La Trobe University

We may take it for granted that the sex of an animal is established at birth and doesn't change.

However, about 500 species of fish change sex in adulthood, often in response to environmental cues. How these fish change sex has, until now, been a mystery.

The secrets of fish that change sex have, for the first time, been revealed by an international collaboration led by New Zealand scientists and including La Trobe University geneticist and Prime Minister's Prize for Science winner 2017, Professor Jenny Graves. The findings were published today in the prestigious journal, Science Advances.

"I've followed the bluehead wrasse for years because sex change is so quick and is triggered by a visual cue," Professor Graves said.

"How sex can reverse so spectacularly has been a mystery for decades. The genes haven't changed, so it must be the signals that turn them off and on."

Bluehead wrasses live in groups, on coral reefs of the Caribbean. A dominant male—with a blue head—protects a harem of yellow females. If the male is removed, the biggest female becomes male—in just 10 days. She changes her behaviour in minutes, her colour in hours. Her ovary becomes a testis and by 10 days it is making sperm.

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