Gila Topminnow

DESCRIPTION:
Gila Topminnow are small, usually less than one inch long, live-bearing (ovoviviparous) fish. Although minnow is in the name, this species is in a distinct family (Poeciliidae) compared to other species known as minnows (family Cyprinidae) in the southwest. The males of the species have a modified anal fin called a gonopodium that is used to transfer spermatophores to the female genital pore for internal fertilization. The gonopodium is long reaching past the tip of the snout when deflected forward in position for copulation. Both males and females have an elongated body, a slightly curved dorsal profile, and a subterminal but upturned mouth. Gila Topminnow have a dark lateral band that is usually continuous from the head to the caudal base. The scales are darkly outlined on the dorsum with patches of melanophores but lack discrete spotting.

DISTRIBUTION & STATUS:
Historically the Gila Topminnow was found throughout the Gila River basin, Arizona and New Mexico, up to 1600 m elevation and at comparable elevation throughout much of the northwestern Sonora. It is extirpated from much of it former range in the U.S., persisting naturally in only a few isolated stream segments and springs and federally listed as endangered. The disappearance of Gila Topminnow is largely attributable to environmental changes stemming from human activity. Livestock grazing and timber harvest began to alter natural vegetation before the 1800s, in turn changing the patterns of runoff, erosion, sedimentation, etc. Intensive development for irrigated agriculture commenced in the 1800s, further modifying flow patterns and discharge volumes of streams. In the 1940-50s introduction and establishment of myriad non-native species began to restructure aquatic communities, influencing the faunas of whole watersheds.

HABITAT:
They prefer shallow, warm springs or slow-moving waters, but can tolerate a wide range of temperature and current regimes.

FOOD HABITS:
Primarily omnivorous, consuming detritus, algae, amphipods, ostracods, and insect larvae.

REPRODUCTION:
Breeding usually occurs between January and August. During breeding season, males are often black with a golden streak along the pre-dorsal midline and an orange or red orange patch at the base of the gonopodium and often at the base of the dorsal fin. Breeding females develop intensified body pigments overall and a conspicuous jet black region surrounding the anus. Generally, Gila Topminnow live one year, with sexual maturity occurring as soon as two months.