Xenotoca

The redtail goodeid, Xenotoca eiseni, is a livebearer from Mexico, found in habitats from clear mountain streams to polluted roadside ditches. Very hardy and adaptable, it is less popular in the hobby than it once was, probably because of its often aggressive nature. Some specimens attack and kill other fish, catfish in particular, so a species tank is best. As in other goodeids, the developing young are nourished by a structure known as the trophotaenia.