Size Matters in Fish Mating

February 14 , 2007

When it comes to mating, dominant green swordtail fish let their tails do the talking.

Female green swordtail fish mature faster sexually when they see males with larger-than-usual tails, according to research in the United Kingdom.

Scientists at the Universities of Exeter and Glasgow say it demonstrates for the first time that sexual maturation can come in response to visual clues.

"While our study focused on green swordtail fish, it seems unlikely that this attribute is limited to this one species," said Craig Walling of the University of Exeter's school of biosciences.

Environmental effects on sexual maturation were previously assumed to be as a result of direct interactions, such as aggressive behaviour by dominant males and females.

But for male green swordtail fish, such behaviour isn't even necessary when dealing with competitors.

The sight of an alpha male also had the reverse effect on younger green swordtails, retarding their maturation until a better time emerges with less competition.

The fish were kept in separate tanks so while they could see each other through the glass, they could not use other senses to respond to one another.

The fish, native of North and Central America, are named for the striking tail fins of the males.

The authors published their report on Valentine's Day in the UK journal Biology Letters.

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