Mosquitofish Genital Size Not A Factor In Mate Selection

Mosquitofish are considered pests in Australia, thanks to a failed introduction in which some thought the fish would help to control mosquitoes. But since then, the fish are relatively unwanted there, making them a great specimen for scientific study.

In an example of this, researchers at the Australian National University have recently used the fish as a subject to investigate the role of fish genital size in mate selection. Their findings are useful in understanding the evolution of genitalia.

Mosquitofish have sexual organs called a gonopodium. The normal male gonopodium is equal to about 30 percent of the mosquitofish body length.

To test the theory that bigger genitals make male mosquitofish more attractive or successful in fathering offspring, scientists at the university devised an experiment. It began with them selectively breeding fish so that their offspring would have larger or smaller gonopedia. This took place over the course of eight generations.

Male mosquitofish with different size genitals were allowed to freely compete to mate with females. The research used a sample size of 173 males and 165 females.

From there, scientists used paternity testing on over 2,500 offspring to find which males had been successful and which ones hadn’t. The results didn’t lean far either way, as investigators concluded that female mosquitofish don’t seem to have a preference.

The findings showed that the size of male genitals had no effect on their attractiveness, success in
reproduction or their ability to swim and move around in the water. They contradict another study from scientists at the same university that found a positive relationship between fish paternity success and genital size.

Mosquitofish have live offspring rather than lay eggs. Males of the fish use modified anal fins (gonopodium) to inseminate females.

Full findings of the research, as well as methods and figures, have been published in the journal Nature Communications.

Mosquitofish. (Credit: Stuart Hay / Australian National University)

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