There's an old adage that warns against passing judgment based on appearance, but female bluefin killifish, like many animal species, apparently don't share such human wisdom when choosing a mate.

In the game of love, we typically think of males as being the showy courting sex and females being the coy choosy sex. But what if your species doesn't have the simple division of males and females?

Researchers used male replicas of bluefin killifish and controlled their movement with robotic arms to improve repeatability in experiments designed to determine how fertile female fish would respond ...