By ANNE BESTON
Size doesn't just matter to female crayfish, it tops the list.
Auckland University PhD student Natalie Raethke has been studying the sex lives of two common species of crayfish as part of her research into chemical communication between the crustaceans.
Her findings could provide important clues as to how
crayfish can be bred in captivity.
New Zealand's crayfish export industry is worth about $120 million a year, and the project could increase this.
Ms Raethke released up to 20 crayfish, both red rock lobster (jasus edwardsii) and packhorse lobster (jasus verreauxi), in a series of tests to find out how they communicate and how they decide on a sexual partner.
Given a choice, large female crayfish will head for the largest males every time.
"If a large female finds a small male there is a chance there won't be enough sperm for all the eggs she produces," Ms Raethke says.
"She will mate with a small male but only if she doesn't find anyone else."
While you might think crustacean reproduction would be a fairly run-of-the-mill business, the sex life of crayfish is anything but boring.
The male and female go through a long and intense courtship ritual, sitting facing each other for several days waving their antennae.
Ms Raethke says this process is thought to be linked to smell.
"They're checking each other out and then the female basically makes the choice."
Once they decide to mate, the male crayfish will flip onto his back, the female climbs on top and they go into a tight clinch.
The male produces a sperm sac, or spermatophore, which the female "scratches" over her eggs to fertilise them.
The eggs are held in small hairs, called setae, around her tail.
For six months she carries the fertilised eggs around with her as the larvae grow and develop.
When she releases the larvae, they flow in ocean currents for up to two years before becoming fully developed crayfish.
Ms Raethke also carried out experiments on crayfish urine, using tanks with male urine, female urine and seawater.
Female crayfish headed for the tank containing the males' urine.
"I have shown lobsters have these chemical responses and that's quite new," she says.
Ms Raethke is a German student on a scholarship to Auckland University.
She expects to complete her PhD next year.
nzherald.co.nz/environment
