Basolo, associate professor of biological sciences at the University of Nebraska, told Animal Planet News that the loser really looks the part.

"His body darkens, due to a stress response, he puts his head down and he then positions himself at the periphery of the tank," she said, and added that the loser even folds in his fins.

Brian Trainor, a postdoctoral researcher in the College of Social and Behavioral Sciences at Ohio State University, told Animal Planet News, "One part I was a bit amazed with was that in the sword manipulation experiment, somehow the fish were able to determine their own artificial sword sizes," he said.

Trainor added, "I think people usually think that fish are not too bright. Not only were these swordtails able to assess their competitors' apparent sword length, but also they were able to compare that with their own sword length. I thought that was a cool result."

He even believes there is a swordtail-human link, since both species seem to have evolved traits and behaviors that do not offer any apparent survival benefits.

The sword, for example, appears to be useless, save for its visual impact. For humans, he said possible examples include artistic abilities and senses of humor.

Like male fish showing off their swords to females, he suggested that these human abilities might exist, in part, to impress members of the opposite sex. Like the fish swords, they can also weed out competitors who may not be as talented or humorous.

Trainor added, "Our studies in swordtails show that sexually selected traits can be complex and used in multiple behavioral contexts, much like many aspects of human behavior."

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Name: Green Swordtail (Xiphophorus helleri)
Primary Classification: Poeciliidae (Livebearers and Topminnows)
Location: Mexico to Honduras
Habitat: Warm springs, weedy canals and ponds
Diet: Mainly aquatic plants and insects
Size: Up to 5 inches in length
Description: Green above; females have dark scales on back and sides and yellow belly; males have dark stripe on side, red belly and long, yellow-orange to red-colored tail shaped like a sword
Cool Facts: Males use their swords as visual signals during fights; the male with the larger sword can often chase the smaller fish away before blows are exchanged.
Conservation Status: Common

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