Redtail Splitfin

About

The redtail splitfin (Xenotoca eiseni) is a goodeid livebearer native to freshwater systems in western Mexico, and it comes with a reputation that deserves respect. Males develop a warm reddish-orange flush toward the tail, which gives the fish its common name, while females are more subdued in coloration. As is typical for the family. Size differences between the sexes are less pronounced here than in most livebearers, and researchers think this relates to the mechanics of goodeid mating, where compatible body sizes help the reproductive structures align properly. Speaking of reproduction, goodeids are genuinely different from other livebearing fish. Females cannot store sperm, so each brood requires a fresh mating. The developing young are nourished internally through a placenta-like structure called a trophotaenia, and newborn fry sometimes arrive with a small cord-like remnant attached. Completely normal, and gone within a few days. The fry are large and confident from birth, eating the same foods as adults immediately. Where this fish gets complicated is temperament. Some individuals settle fine in a community, but others will harass or outright kill tankmates, with catfish being particularly at risk. Keeping them in a species-only setup is the sensible call, and it lets you appreciate a genuinely underrated fish without the worry.