Gila Topminnow, Poeciliopsis occidentalis occidentalis
Note: This Species is currently considered to be ENDANGERED and if encountered should be handled accordingly.
Gila Topminnow, Poeciliopsis occidentalis occidentalis. Fish collected from the Agua Fria River in Peoria, Arizona, April 2018. Length: 3.8 cm (1.5 inches). Fish was immediately photographed and quickly returned unharmed to its native environment.
The Gila Topminnow, Poeciliopsis occidentalis occidentalis, is one of two subspecies of the Gila Topminnow, Poeciliopsis occidentalis, and is a member of the Livebearer or Poeciliidae Family, that is also known as charalito and in Mexico as guatopote de Sonora. Globally, there are twenty-four species in the genus Poeciliopsis, of which nineteen are found in Mexican freshwater systems that feed into the Atlantic and/or the Pacific Oceans.
The Gila Topminnow has an elongated curved body that is dark dorsally transitioning to white ventrally with scales that have dark outlines and with a dark band on their sides. Breeding males are black in color with yellow fins. Their head is large and flattened with a small slightly upturned mouth with large eyes. They have large prominent bellies and their fins are without spots, a key to their identification. Their anal and dorsal fins are small, opposite, and small in stature; their caudal fin is large and slightly rounded. They reach a maximum length of 6.0 cm (2.4 inches) with females being larger than males.
The Gila Topminnow is a non-migratory freshwater species that is found in heavily vegetated shallow, warm, quiet water including ditches, irrigation canals, ponds, and streams. They are very adaptable and capable of surviving water temperatures of between 0oC (32oF) and 38oC (100oF), in waters with high salinities and can survive without water for up to two days by burrowing into the mud. This species is an opportunistic omnivore that feeds on amphipods, detritus, small crustaceans, small fishes, insect and specifically mosquito larvae, ostracods and vegetation. They are known to cannibalize their young. In turn they are heavily preyed upon by shore birds including Herons. Reproduction is viviparous and involves internal fertilization, gestation periods of 24 to 28 days, giving birth to 10 to 15 live young. The females can store spermatozoa for several months and may produce up to 10 broods after being isolated from the males, and carry two broods simultaneously. The males vigorously defend mating territories and court females. They reach sexual maturity within two months of birth. They have life spans of one year.
The Gila Topminnow is a native to the Gila River basin and the Ríos de la Concepción in Sonora northwest Mexico at elevations below 1,200 m (4,000 feet).
The Gila Topminnow is very similar to the Yaqui Topminnow, Poeciliopsis occidentalis sonoriensis, which is found in the Yaqui River. They are also very similar in appearance and in body structure to several other poecilids.
From a conservation perspective the Gila Topminnow in currently considered to be of Least Concern. However, in some parts of their native range, and specifically in Arizona they are considered to be ENDANGERED with significantly declining populations. Their long-term viability is threatened by human development that changes their native habitats (pollution and water flows), and via the introduction of the Western Mosquitofish, Gambusia affinis, that prey on their juveniles. Efforts to reintroduce them in several areas and now on-going.