PARIS - SEX among electric fish in the Congo River is a rather charged business, according a to new study reporting on an unusual experiment.

Mormyrids are fish that use low-voltage discharges from an electrical organ to hunt for food in chocolate-brown river water.

Intrigued as to how these unusual creatures locate each other for reproduction in almost zero visibility, a German team replicated the mood for mormyrid lurv in a tank on the outskirts of Berlin.

Six females from the species Campylomormyrus compressirostris were shipped in from Kinshasa, capital of the Democratic Republic of Congo.

'All males showed a kink in their anal fin base indicating sexual maturity,' the study recounts, a touch breathlessly.

'Prior to the experiments, females were isolated, and breeding conditions were achieved by simulating low conductivity, rainy-season conditions.'

The females, all ready to spawn, were placed at night in the middle of a large tank with a small zone at either end that was sectioned off with a grill.

In a first set of experiments a male was placed in each of the two segregated areas.

One of the males was, like the female, a C. compressirostris. The other was of a closely related species, C. rhynchophorus, whose males are physically similar to C. compressirostris but send out a much weaker electrical signal.

An infrared camera kept track of the females' movements, and showed - not surprisingly - that the gals were more attracted to their own kind.

In a further set of experiments, the second male came from a third species, C. tamandua, whose males are physically quite different to C. compressirostris but emit an almost identical electrical signal.

This time, the females showed the same interest in the signals as they did for a male from their own species, suggesting that - as in human love - it's the electricity that counts.

The study, led Ralph Tiedemann of Potsdam University, appears in Biology Letters, published Wednesday by Britain's Royal Society. -- AFP