Getting In Touch With Eels' Feminine Side

December 8, 2005

Release from: Beck Eleven
The Press (New Zealand)

Scientists are investigating whether contaminants in Lake Ellesmere could be responsible for gender-bending among eels.

Environment Canterbury (ECan) has contracted Landcare Research to study the reproductive organs of eels and flounder.

The aim is to discover whether intensive dairying or other factors could be responsible for the disproportionately high number of female eels in the lake.

While the sex of other fish is determined by genetics, the sex of an eel is determined by its environment.

A high density of eels will naturally cause 99 per cent of them to be male.

Landcare Research ecotoxicology programme leader Louis Tremblay and scientist Dr Cara Lowe yesterday started taking blood samples from eels in the lake.

Tremblay said the issue of contaminants in the environment had sparked overseas studies where it was shown that industrial and farming effluent could manipulate the sex of eels and fish.

He said little information was available in New Zealand and hoped this study would throw some light on the effects of these "endocrine disrupters" – contaminants which inadvertently influence gender.

Tremblay said it was possible that large numbers of cattle grazing at the water's edge could leech estrogen into the lake and feminise the eels.

"We, as humans, have our waste treated but animals' is not treated and might be a potential source.

"The lactating status of the cows might mean a fair amount of hormones."

He said eels were a complicated species to work with. They did not sexually differentiate until they were 20 years old and could live up to 40 years.

ECan surface water quality scientist Shirley Hayward said the initiative came from questions raised by the community about effluents and the high concentration of chemicals in the lake.

Results from the $5000 study are expected early next year.