Gila longfin dace
The official name for this Arizona native fish is the Agosia chryogaster chryogaster, and it 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.
Description
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 65mm. 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 noticing 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 typically has silvery gray upper portions and olive lower portions, 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 habitat, and it has also increased the capabilities of the fish. They are generally found at elevations less than 4900 feet, with some scattered outlying records of species above 6700 feet.
Habitat
The 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 desires relatively warmer water, with an average temperature preference of 75 degrees Fahrenheit. They also prefer water depths averaging 0.6 feet. During water shortages, they will seek refuge in algae and detritus mats of wetland habitats.
Reproduction
These freshwater Daces will usually spawn during the months of September to December, and will also extend this window into January for low 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 length and mating success.
Biology
Sediment discharge in river bottoms occurs during flooding seasons, and will cause the 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.