Swim away from the female, sucker

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By Stuart Colcleugh

The typically deep-dwelling sucker breeds in shallow water, and if another amorous male appears in the breeding area the fish rapidly rolls its eyes, exposing the top third of its eyeballs. Sunlight shining through the shallow water bounces off the exposed eye surfaces, reflecting strong ultraviolet rays toward the other fish—rays that don't penetrate to deeper water.

Novales Flamarique, an expert on fish neuroanatomy, suspected that the sucker's flashing eyes serve as a territorial warning mechanism.

So he tested the theory by positioning counterfeit fish with LED eyes at the perimeters of a tank and placing a group of razorback males in the middle. Sure enough, every time he flashed the fake fish eyes the real suckers bolted away.

Novales Flamarique published a decidedly more technical and precise description of his findings in a recent volume of Britain's Proceedings of the Royal Society.