Spottail Killifish, Pseudoxiphophorus bimaculatus
Spottail Killifish, Pseudoxiphophorus bimaculatus. Caught from the Río Cuautla, Morelos, February 2017. Length: 5.8 cm (2.3 inches). Catch, photograph and identification courtesy of Ben Cantrell, San Diego, California.
Spottail Killifish, Pseudoxiphophorus bimaculatus. Caught from the Río Cuautla, Morelos, February 2017. Length: 6.2 cm (2.4 inches). Catch, photograph and identification courtesy of Ryan Crutchfield, Tampa, Florida.
Spottail Killifish, Pseudoxiphophorus bimaculatus. Caught from a coastal stream in Beliez, June 2012. Length: 6.2 cm (2.4 inches). Catch, photograph, and identification courtesy of Josh Leisen (joshadventures.com), Gaylord, Michigan.
The Spottail Killifish, Pseudoxiphophorus bimaculatus, is a member of the Livebearer or Poeciliidae Family, that is also known as the Twospot Liverbearer and in Mexico as guatopote manchado and topote de dos puntos. Globally, there are seven species in the genus Pseudoxiphophorus, of which six are found in the Mexican freshwater systems that drain into the Atlantic and/or Pacific Oceans.
The Spottail Killifish has a small elongated body. Their head is large and flattened with a small upturned protrusible mouth and large eyes. The females are a drab gray-green and the males are brightly colored red. The Spottail Killifish is sexually dimorphic with females being larger than males with a maximum of 15 cm (5.9 inches) in length versus 7.0 cm (2.8 inches).
The Spottail Killifish is a non-migratory freshwater species that is found in in standing water that include ditches, lakes, marhes, ponds, and seasonal ponds, and in slow moving water that include brooks, creeks, rivers and streams at elevations in excess of 1,000 m (3,280 feet). They can also be found in saltwater environments with salinities of less than 7 parts per thousand. They prefer water temperatures between 20oC (68oF) and 28oC (83oF). They are surface feeders that consume detritus, small insects and insect larvae, and zooplankton near the surface. Reproduction is viviparous and involves internal fertilization, a 6 to 8-week gestation period, with each female giving birth to 20 to 100 live young. They reach sexual maturity within twelve months of birth. In the wild females outnumber brightly colored males from 2:1 to 6:1 presumably due to predation and hypoxia during high temperature episodes. They are know to be plagued by at least one parasite sourced from introduced Nile Tilapia. The Spottail Killifish is poorly studied with very limited information available about their lifestyle and behavioral patterns including specific details on age, growth, longevity, movement patterns, diet, habitat use, and reproduction.
The Spottail Killifish is very similar in appearance and in body structure to several other poecilids but they are the only poecilid that has a large spot on the upper base of their tail.
The Spottail Killifish is native to the freshwater systems of Mexico within the States of Campeche, Chiapas, Oaxaca, Quintana Roo, Tabasco, Veracruz and Yucatán that drain into the Atlantic Ocean. They have been recently introduced to the freshwater systems within the States of Guerrero, Jalisco, Michoacán and Morelos that drain into the Pacific Ocean.
From a conservation perspective the Spottail Killifish is currently considered to be of Least Concern with stable, widely distributed populations. In some of the areas where they have been introduced, they have become highly invasive. They are utilized at a minimal level by the aquarium trade as they are very easy to maintain, prolific breeders in captivity and active swimmers. Their long-term viability within their native range is of concern due to habitat loss and degradation.