Xenophallus umbratilis

Common Name: Olomina
Latin Name: Xenophallus umbratilis (formerly Neoheterandria umbratilis)
Origin: Central America
Temperature: 72-78º F
Ease Of Keeping: Moderately Easy
Aggressivness: Not Aggressive
Lighting: Any
Adult Size: Males to about 1″, females to 1.5″
Minimum Tank Size: 5 gallon
Feeding: Will take commercial foods, particularly enjoys live foods.
Spawning Method: An easy to breed livebearer. They will eat their young, so take steps to save the young if you want to raise them.

Xenophallus umbratilis (formerly Neoheterandria umbratilis) is a somewhat small and more delicate livebearer. The females reach a size of about 1.5″ in length, with the males staying at about 1″ long or less. They are fairly plainly colored, with a plain olive body, and a dark dorsal fin. When in good condition, the males bodies can become a fairly bright yellow color, though the females always look about the same. They can also have some faint vertical stripes on the back half of their body. These stripes are most obvious in the young, though some of the adults have them as well. Even though they do have a very plain coloration they are still a somewhat attractive fish, though definitely not showy.

The name Xenophallus was given to this fish because of it’s unusual gonopodium. It has a series of hook like structures that are easily visible with the naked eye. This is also the main reason why they where re-categorized out of the Neheterandria genus.

This species is fairly hardy, but they can be a bit shy, and the fry are sometimes difficult to raise. (I believe that they are significantly more sensitive to ammonia than most fish.) They will readily accept flake food, but are a bit more reluctant to eat it compared to other fish. They also like baby brine shrimp and will take fruit flys once they are large enough. In the virgin tank that I have set up for these fish the females are always hiding in the moss, while in the population tank they are much less shy.

I have also had some trouble in bringing them in from the wild. We brought in between fifty and seventy-five fish toward the end of June 2007, and separated them into four tanks (three ten gallons and one twenty long.) There were minimal deaths for the first few weeks, and then suddenly two of the tanks crashed. I did a 50% water change on the tanks, and medicated with an antibiotic and anti-fungal (there were no obvious signs of illness) and the deaths stopped. One of these tanks was the 20L, which was an older steel frame tank that was leaking slightly. At least three ten gallon tanks below it, all containing fish from the genus Brachyrhaphis (most of which were Brachyrhaphis rhabdophora), showed no signs of illness despite no action being taken.

Later (a week to a week and a half after the first two tanks) another tank crashed, and all of the Xenophallus umbratilis died before any action could be taken. However, there were a few stray fish, probably from the genus Brachyrhaphis, that showed no ill effects at all. I had done a water change on this tank at the same time as the other two infected tanks, but used different equipment in order to assure no cross contamination. (This tank was located next to the 20L.)

The fourth tank never had this issue, and I also did a water change on it at the some time as the other tanks.