Gila Trout (Oncorhynchus Gilae)

Gila trout

The Gila trout (Oncorhynchus gilae) was first discovered in 1908 when the Arizona Game Warden, Joe Sawhill found it in the Gila River, hence the name of the fish. What makes this fish so special is that it’s one of the only trout species to live entirely within the U.S., and it has been protected under the Endangered Species Act since 1967 due to overfishing, drought, and human development along its habitat.

Since its discovery in the early 20th century, the Gila trout (Oncorhynchus gilae) has been one of North America’s most endangered fish species. It was also the first fish to be listed as endangered under the U.S. Endangered Species Act in 1967, an act that requires federal agencies to avoid harming or otherwise impacting listed species and their habitats whenever possible.

But despite being protected from illegal collection and harm by federal law, this fish continues to face major threats to its survival through habitat destruction and degradation, as well as climate change and drought.

In the United States, there are three species of trout native to the desert southwest: Apache trout, Gila trout, and Chihuahua trout. Of these, only Gila trout can be legally taken from wild populations by anglers in New Mexico and Arizona, and its popularity as a game fish has led to a significant decline in the species’ numbers in both states.

Origin and descriptions

Gila trout

The gila trout, also known as Arizona trout, are native to Arizona and New Mexico and are often found in cool, spring-fed streams between 5,000 and 8,500 feet above sea level. Their range extends from Springerville in eastern Arizona eastward to Santa Fe and Albuquerque along the Rio Grande River. The typical habitat includes large springs of clear, cool water that flow into tributaries of major rivers such as Rio Grande or Little Colorado River.

This species has been introduced elsewhere but has not established self-sustaining populations. In Arizona, they have been introduced into Big Bug Creek near Clifton and Upper San Francisco Creek near Flagstaff. These introductions were made with federal permission to provide additional protection for endangered fish species downstream in Grand Canyon National Park.

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Species profile

The Gila trout belong to the family Salmonidae, subfamily Salmoninae. They are members of a group of fish called trout that are native only to North America. Gila trout are also referred to as gilas or chars and are listed as threatened under both state and federal law.

There is only one species in existence today, Oncorhynchus gilae, which is found only in Arizona and New Mexico in the southwestern United States. It was originally found in parts of California, Nevada, Utah, and Colorado but has been extirpated from these areas. In fact, it’s believed that less than 100 individuals remain in their natural habitat.

Scientific name

The scientific name of the Gila trout is Oncorhynchus gilae


The gila trout lives in habitats with soft sedimentary substrates like springs, high altitude lakes, and tributaries. The streams have moderate to fast flows that are warm to cold, ranging from 70 degrees F in winter to 86 degrees F in summer. It is one of only two species endemic to Arizona, meaning it is found nowhere else on Earth. The other native fish of Arizona’s spring systems is the Apache trout, Oncorhynchus apache.

Gila trout are endemic to two rivers—the San Francisco and San Carlos. In order to preserve their habitat, it’s important to understand exactly what types of living spaces they prefer. They tend to prefer cool waters and small, shallow pools in which they can hide from predators. They are less likely to appear around large bodies of water or rivers that have strong currents or drop off quickly at their edges, where predators (like bass) may lurk.


The Gila trout can range in size from 11.8 inches (30 cm) to a maximum size of 21.7 inches (55 cm) in length.

Tank size

Due to their large size, the minimum recommended tank size is 250 gallons (946 liters).

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Tank requirements

Although most aquarium fish can be housed in 10-50 gallon tanks, keeping gila trout in smaller containers is not advised. They are schooling fish and need plenty of space for swimming and foraging. Minimally, you’ll want to have at least one 250-gallon tank for these fish. Their water should be kept warm, between 73 and 84 degrees Fahrenheit, with pH levels ranging from 7.4 to 8.0 (slightly acidic).

The tank should also be well-filtered and cycled before adding any fish to it. The substrate should consist of river rock or fine gravel, as sand will likely get into their mouths when they eat food that has fallen on the bottom of their tank. In addition, you will need a heater, filter, thermometer, and aerator for your tank.

A darkening hood is recommended for aquariums housing adult gila trout, as light tends to stress them out. You will also need an air stone to help keep oxygen levels high in your tank.

Finally, make sure you have an appropriate lid for your tank; if it doesn’t already come equipped with one, you can buy a screen lid or cover made specifically for fish tanks online or at pet stores.

Tank mates

A Mexican desert pupfish may be best for your gila trout. The pupfish is not as aggressive as some other species and is known to coexist well with others in an aquarium. Other fish that live peacefully with a gila trout include neon tetras, cherry barbs, corydoras catfish, and bettas. Keep any fin-nipping fish away from your trout, such as tiger barbs and goldfish; they can do serious damage to its delicate fins.


Gila trout

A gila trout can lay hundreds of eggs every year, so it’s no surprise that these fish are popular among aquarium owners. As long as you provide adequate space and oxygen levels, these fish can reproduce on their own.

Adult gilas are territorial when breeding and may become aggressive to any other individuals in their tank; male gilas will even turn on females if they try to spawn with another male. To avoid unnecessary aggression, keep only one pair per tank.

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This species is also known for its cannibalistic tendencies: If food is scarce or if an individual feels threatened by others in its tank, it might resort to eating its young. Keep an eye out for fry (baby fish) that appear stunted or malnourished—if you notice any, be sure to remove them from your tank before they get eaten by their parents!

Fry tend to hide among rocks and plants during feeding time, but adult gilas have poor eyesight and may not recognize them as something edible. Make sure all fry are fed at least twice daily until they grow big enough to join their parents at mealtime.

Are they aggressive or peaceful?

While young gila trout can be aggressive, most adults are peaceful. They don’t bite as adults and only use their large teeth for tearing apart prey. While some have described them as friendly, they do not thrive when kept with other fish or in community tanks. If you’re interested in keeping a gila trout in an aquarium setting, it’s best to keep one on its own.


Gila trout

For a fish that’s evolved to live in water that can reach 90 degrees Fahrenheit and has no scales or true fins, gila trout (Oncorhynchus gilae) care is surprisingly easy. The fish requires only a tank of room-temperature freshwater and an air pump to oxygenate its habitat. Provide it with rockwork and hiding places, which will help mimic its natural environment.

A pH level between 6.0 and 7.5 should be suitable for most individuals, although some hobbyists have reported success keeping these fish at levels as low as 5.0; use your test kit to determine whether your particular species thrive at a specific pH level before making any adjustments to your tank’s chemistry.

A temperature between 70 and 80 degrees should suffice for most specimens; if you keep multiple individuals together, you may need to adjust accordingly based on their individual tolerances for heat.

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What they eat

They are carnivorous, feeding on insects and small fish. In captivity, they will eat most commercially available trout foods. Frozen foods such as bloodworms and brine shrimp can be offered as well. Commercial trout pellets should be avoided because of their high protein content; these fish have very little tolerance for excessive protein in their diet

The diet may also consist of mayflies and other small aquatic invertebrates, such as stoneflies and midges. They also eat various small fish and smaller trout, as well as aquatic arthropods. They have been observed attacking prey animals several times their own size. When not consuming insects or other aquatic organisms, they subsist on a diet of crustaceans.


Gila trout

Gila trout can live for 5-9 years with good care and proper water conditions.

Parasites and diseases

Oncorhynchus gilae is considered to be very susceptible to bacterial infections as well as parasites. Parasites are one of the more significant threats to their life and can result in death if not treated properly. Because they lack scales and bony armor, they are prone to external parasites that feed on their skin. Larger fish are especially at risk of parasite infestation and should be watched closely for early signs of sickness or external symptoms.


The gila trout is endemic to two of Arizona’s rivers: The San Francisco and its major tributary, Sonoita Creek. Both are prime habitats for tiger and bull sharks, which prey on both juvenile and adult gilas in their environments. These predators also make their homes near these rivers’ warm waters, so they pose an immediate threat to both species of trout.

Do they make good pets?

A gila trout makes an interesting pet, but they are not easy to take care of. They live in very shallow and extremely fast-moving water, so they need an aquarium with at least 15 gallons of water. You can put driftwood or even rocks in your tank for them to hide behind and make it more comfortable for them. The temperature needs to be between 60-70 degrees Fahrenheit.