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Brenton Stacey
Public relations officer

Research by an Avondale College lecturer may bring more stability to the social life of a sex-changing fish.

Jason Morton has received a PhD from the University of Newcastle for his four-year study of crimson-banded and Maori wrasse at Catherine Hill Bay and Norah Head on the Central Coast. He found the fish begin life as females but become males at age four or five years. They then live in a harem of up to 10 socially ranked females with the largest, highest ranking female likely to be the one to change sex after the male dies. Promiscuity is popular with females visiting other harems to determine whether joining will improve their rank.

Enter the zealous fisher who can eliminate the only male in a territory. "The bag limit is 20 fish per person per day, but if you bring a mate, that's 40, which could result in removing all males in a large reef," says Dr Morton. If so, the highest ranked female in a harem changes sex and the remaining females re-contest their rank. The process takes about three weeks, "but in that time, the territory might be fished again," says Dr Morton. He describes wrasse at Norah Head as more "skittish" than those at Catherine Hill Bay, which is less regularly fished.

Crimson-banded wrasse can live at least 10 years and Maori wrasse at least 13, partly because they have no known natural predators and prolong life by wisely using resources--each species eats similar food but in different proportions and spawns in different seasons.

The 300 hours Dr Morton spent under water has helped him identify individual fish by using unique facial and body markings. He has even named some of the fish--Golf swing, Small circle, V-head. "You can't interview a fish," he says, "so you have to spend a lot of time following them around."

Caption: Jason Morton's wrasse study reveals the fish changes sex to climb the social ladder.
Credit: Gilmore Tanabose