Gila Trout
The Gila trout, native to the waters of Arizona and New Mexico, is a distinctive fish recognized for its dark olive-green back that transitions to a golden-yellow belly, a feature unique to true Gila trout. Initially classified as part of the cutthroat trout family upon its discovery in 1950, further research revealed it to be a distinct species within the Oncorhynchus genus. Gila trout typically grow up to 22 inches (55 centimeters), although sizes of 12 inches (30 centimeters) or less are more common. They thrive in fast-moving, rock-bottomed rivers but have also been successfully introduced into various other aquatic environments.
This species primarily feeds on insects, larvae, small fish, and even frogs, and it spawns in late spring and summer, laying about 150 eggs in gravel nests called redds. Gila trout populations have faced threats due to habitat loss and competition from introduced fish species, leading to their classification as a threatened species. Conservation efforts have strengthened their populations in certain regions, particularly in Arizona and New Mexico, where regulations on fishing help protect their numbers until they recover. The lifespan of Gila trout typically ranges from four to six years, and their unique adaptations and breeding behaviors make them a fascinating subject of study for aquatic biodiversity.
On this Page
Subject Terms
Gila Trout
The gila trout is native to the waters of Arizona and New Mexico. The gila trout was discovered in 1950. At first, the fish was thought to be a member of the cutthroat trout family due to its appearance and the place where it was found. Upon closer examination, it was determined to be an entirely different fish.
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Salmoniformes
Family: Salmonidae
Genus: Oncorhynchus
Species: Gilae
The gila trout is dark olive-green along its back, gradually changing to a golden-yellow on its belly. The yellow color is only found on true gila trout and not those that have cross bred or mated with another species of trout. Tiny black spots are present along the sides of the fish. It has a long adipose fin and a long head and upper jaws. The gila trout can reach a length of 22 inches (55 centimeters), although a length of 12 inches (30 centimeters) or less is more common.
The gila trout lives in the fast-moving waters of rock-bottomed rivers. It has adapted well to other areas where it has been introduced, including reservoirs, lakes, ponds, streams, and canals.
The gila trout does not have lungs like other animals. It receives the oxygen it needs from the water. It takes large amounts of water into its mouth which it then passes over its gills. The gills remove the oxygen, allowing the wastewater to pass out of the fish through its gills.
Due to the gila trout's tendency to crossbreed, or to mate with other species of fish, the population of true gila trout has sometimes dropped considerably. When the population drops too low, the government does not allow the fish to be caught by anglers, or fishermen, until they are able to reproduce enough so their numbers rise to a level at which the population is no longer endangered.
The gila trout lives on a diet of insects and larvae. It finds larvae on the bottoms of rivers and lakes. It also feeds near the water's surface, taking insects, nymphs, and flies which land there. The gila trout also eats small fish, frogs, tadpoles, and worms. Some of the larger gila trout eat the young fish of their own species.
The gila trout spawns, or produces offspring, in late spring and summer. The female trout chooses a location near the mouth of a stream. She makes shallow troughs, or holes, called redds, in the gravel into which she lays her 150 eggs. The male then fertilizes them with his sperm, called milt.
How quickly the eggs hatch depends on the water temperature, with warmer temperature causing the eggs to hatch more quickly. The newly hatched trouts are called alevins. The alevins obtain nourishment from yolk sacs which are attached to them at birth. When the young begin swimming, they are called fry. Fry are very vulnerable to predators, and very few make it to adulthood.
The life span of the gila trout is an average of four to six years. The gila trout is considered a threatened species due to habitat loss and the human introduction of game fish. However, it was considered endangered in the early 2000s. Populations of the fish introduced into streams and rivers in Arizona and New Mexico have bolstered, or strengthened, the population of gila trout in those regions.
Bibliography
“Gila Trout (Oncorhynchus Gilae) - Species Profile.” Nonindigenous Aquatic Species, 4 Sept 2019, nas.er.usgs.gov/queries/factsheet.aspx?SpeciesID=905. Accessed 27 Mar. 2024.
McReynolds, G. “Gila Trout Recovery & Angling.” New Mexico Game and Fish, 2024, www.wildlife.state.nm.us/fishing/native-new-mexico-fish/gila-trout-recovery-angling. Accessed 27 Mar. 2024.