Description

The Gila Longfin Dace (Agosia chryogaster chryogaster), is the only Agosia species found in Arizona. The only other form of fish closely related to Agosia is the Rio Yaqui, which also occurs in Arizona. The body of the fish is “Fusiform”, meaning it has very small scales that travel laterally along the body. A typical Gila Dace has an average length of 3.5 inches. Their mouths are small and oblique, with a very bluntly shaped snout and head. The nares or outer “nostrils” of the fish direct water toward the gills and define the termination of the mouth. The Gila Dace is easily distinguishable from other cyprididae by the lack of dark spots normally located on the triangular dorsal fin. There is however, a large black spot at the base of the caudal fin. This fish is typically silvery gray dorsally and olive ventrally, with the absence of gold speckles found on its relative, the Yaqui Longfin Dace.

Distribution in Arizona

The Gila Dace was originally introduced into the Virgin River Basin, the Zuna, and the Membris Rivers. This represents the bulk of the range and overall distribution of the fish, with increasing populations around mountainous areas of the Mogollon Rim. This drastic, rapid increase in range is due to vast climate changes within its range. They are generally found at elevations less than 4900 feet, with some scattered outlying records of species above 2030 meters.

Habitat

The Gila Dace has a very wide range of water temperature preferences, being found from low and hot desert streams, to mountain brooks with extremely cold water. They also prefer brooks and streams that have sandy or gravely bottoms, typically with overhanging banks to protect them from being spotted by predators and humans. The fish prefers relatively warmer water, with an average temperature preference of 23.89 degrees Celsius (75 degrees Fahrenheit). They also prefer water depths averaging 0.18 meters (0.6 feet). During water shortages, they will seek refuge in algae and detritus mats of wetland habitats.

Reproduction

Gila Daces usually spawn during the months of September to December, and can extend this into January in desert habitats.
They reach sexual maturity within the first year of birth, and will create depressions in the sand to hide their eggs.
This helps them provide a safe place for development, allowing minimal disturbance from other species or predators.
Studies have shown a positive correlation between fecundity and fish length,
and it is suggested that the same correlation exists between male body length and mating success.

Biology

Sediment discharge in river bottoms occurs during flooding seasons, and will cause the Gila Dace to swim directly into the currents avoiding the spraying of sediment into the gills. If droughts occur, the fish will also seek refuge in wetland areas such as algae mats. They can prevent desiccation by hiding under logs and stones. The wetlands provide detritus, a nutrient that these fish primarily eat, as the fish are omnivorous and opportunistic feeders. They can also feed on invertebrates, zooplankton, and other forms of algae as the circumstances allow.