A Moment of Science

Fish Blind Dates

There are plenty of examples in nature of females being attracted to the biggest males. Learn about the Atlantic Mollies on this Moment of Science.

There are plenty of examples in nature of females being attracted to the biggest males. This is especially true for a species of fish called the Atlantic Mollie.

The Mollie wants to be as big a fish as possible, because the females show more interest in big fellows than little ones. What’s interesting, though, is what happens with Mollies that live in caves.

The caves that Mollies call home are pitch black. None of the female Mollies can see any of the male Mollies. That could be Arnold Schwarzen-Mollie swimming up next to you, or it could be Mini-Me Mollie; you can’t tell by looking. So which males do you think the female Mollies spent most time around?

The answer might surprise you. When researchers at Hamburg University in Germany studied sexual preference in Mollies that lived in caves, they found the same pattern as in Mollies living outside caves–the females preferred the larger males.

Researchers aren’t yet sure how the fish knew. A good guess, though, is that the cave-dwelling Mollies use organs that sense water displacement. Arnold Schwartzen-Mollie displaces more water than Bill Gates-e-Mollie, so he’ll do better–even on blind dates.

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