Swordtail charachin (Corynopoma riisei) that live in the rivers of Trinidad feast mostly on hapless bugs that plop into the water from surrounding vegetation. In areas where streams flow mostly through forests, the charachin’s main fare is aboreal ants.

For male charachins, size is besides the point: they don’t even have an external sex organ, but they still need to do their thing by somehow fertilizing females internally. So how do you get a female fish to sidle on over so you can slip her your genetic goods? The evolutionary answer turns out to be a fishing line and lure. Over the eons, the male charachins have developed a thin cord that extends from their gill area, on the end of which is an ornament of sorts. When a female bites onto this piece of flesh, she’s in close-enough range and a good position for the male to do the deed.

But how important is the appearance of a male’s lure? A team of researchers, led by Niclas Kolm, of Uppsala University, tested just how well targeted the male’s ornaments were.