Male Swordtail Characins use bait to attract females
Male swordtail characins (Corynopoma riisei) are found in the rivers of Columbia, Venezuela, Trinidad and Tobago. Of course so are the females, so they naturally want to spawn whenever possible. It seems that the males in some of the rivers have evolved a somewhat unique approach to fool their lady into getting close enough to fertilize. They have used the standard fisherman’s trick, a lure. Most fish will hit on a lure that looks like the food they are used to eating, it may be a tube and hook, a bright flashy trolling “fish” or just hand tied fly that looks like some of the insects that the fish in the local fishing hole are consuming. The male swordtails employ the same concept of a lure appendage that entices their female with the false promise they will be getting dinner as well!
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.
Male Swordtail Characins Need the Right Bait
The only problem with this arrangement is that, like the canny fisherman looking to hook the big one, the bait has to be right. The various habitats where these fish are living But the bait changes from population to population, so the lures of the males do as well. This may be a reason that the diversity of the swordtail characins population is so wide. Since these have been available in pet stores, they are available. Experimentation shows that the lures must be specific to the available food in the local habitat, and that having the wrong lure, say for an insect rather than an ant when the food is mainly ants will severely reduce the chances of attracting a suitable female. The result of different staple foods has created a variety of bait and the ones with the best representation seem to be the most successful in mating.