Photo is of a pair of Xenotoca eiseni, Rio Tamazula (the Redtail Goodeid).
This is a nice little fish we’ve had since 2004 when we bought them at an American Livebearers Association auction. They were originally collected from the Rio Tamazula in Mexico by Rusty Wessel prior to that time.
This fish belongs in the family Goodeidae, which has 18 genera and 45 species (some of which are now probably extinct). Goodeids hail from Mexico’s central plateau west of Mexico City. Although considered relatives of the pupfishes, unlike the pupfishes, they are viviparous (livebearing). Goodeids differ from common livebearers such as guppies, swordtails, and platies, since the male goodeids don’t possess a, a penis–like gonopodium. Male goodeids instead have a modified anal fin with a notch or split in the middle of the fin. Reminiscent of killifish mating, goodeid males sidle next to females and press against them to transfer sperm. In another difference with common livebearers, female goodeids have an internal placenta-like structure, the trophotaenia, which provides nourishment to the embryos. Also, goodeid females must mate after delivery of fry in order to produce more fry since they don’t store sperm like the more common livebearers.
I first kept this species (although not the Rio Tamazula population) in the early 1970s while in college. I don’t remember how I acquired them, but do remember peddling them to shops in Austin. One of the shops named them “Tacofish” and sold lots of them. The fish I had then were larger than the Rio Tamazula population, growing to almost three inches. The Rio Tamazula fish don’t grow larger than two inches. The females were drabber than the Rio Tamazula females, which show some orange in the caudal. At some point I lost the original fish, so I was pleased to find the species in the auction.
They are very prolific and we usually have a few hundred on hand and plan to keep them just in case they go extinct in the wild as have some of their relatives.