Rio Grande cutthroat trout

What it is, and why it matters

New Mexico's state fish, and the reason a lot of people finish this challenge differently from how they started it.

The Rio Grande cutthroat is the southernmost cutthroat trout in North America. It evolved in the Rio Grande, Canadian and Pecos basins and nowhere else on earth, which means every one of these fish is in the drainage its ancestors occupied long before anyone drew a state line through it. Ten to twelve inches, usually. Brassy gold along the sides, a hard crimson wash low on the flanks, and a red slash under the jaw that looks, in the right light, like the fish has been cut.

Rio Grande cutthroat now occupy about 12 percent of their historic range. More than 120 conservation populations survive range-wide, more than 80 of them in New Mexico, and a 2013 assessment found 86 percent of those populations sitting in high wildfire-risk country.

Most are small. Most are isolated from each other, above a barrier, in a headwater you could step across, with no way in and no way out. The isolation is deliberate. It is what keeps them alive, and it is also why each population stands or falls on its own.

There is not one big population of this fish with a comfortable margin. There are roughly eighty small ones, most of them in country that burns.

And the headline is good news, worth stating plainly because the wrong version gets repeated so often: this fish is not endangered, and it never has been. It was petitioned for federal listing, spent time as a candidate species, and twice, in 2014 and again in December 2024, the U.S. Fish and Wildlife Service found that listing was not warranted. The second finding explicitly credited the conservation work already done. State agencies, federal agencies, tribes and nonprofits, working the problem for two decades, kept a fish off the endangered species list.

A better story than "endangered," with the advantage of being true. Also the more demanding one, because an outcome like that has to keep being earned.

Identifying it

A red or orange slash under the lower jaw, on both sides. No other trout in New Mexico has it. Gila trout carry a yellow slash; rainbow, brown and brook carry none.

The cutbow problem

Rainbow trout and cutthroat interbreed and produce fertile offspring. The hybrid is a cutbow, and it is common wherever the two have shared water.

A genetically pure cutthroat cannot be confirmed by eye. Not by you, not by an expert, not from a photograph. Biologists use genetics because there is no visual test. Anyone who says they can identify a pure cutthroat by looking at it is telling you about their confidence, not about the fish.

What you can do is shift the odds, in descending order of usefulness.

White fin tips are the giveaway. A pure cutthroat should not have a white tip on any fin. A cutbow often shows white tips on the dorsal, pelvic or anal fins while still carrying a slash. The most teachable tell, and visible in a photograph.

Spot gradient. Cutthroat spots are larger, sparser, crowded toward the tail. Rainbow spots are finer and spread evenly head to tail, including onto the tail fin. A cutbow drifts toward even.

A silvery body with a strong pink lateral band points to rainbow influence. A pure Rio Grande cutthroat is brassy-gold with crimson low on the flanks.

The slash itself is weak evidence. Cutbows usually carry one, just fainter. Faint is suggestive, not diagnostic.

There is a more reliable external key, a small cluster of teeth at the base of the tongue, present in cutthroat and absent in rainbow. It is worth knowing only as the reason biologists rely on genetics. Do not go looking for it. It means putting your fingers inside the mouth of a fish that is about to be released, and no photograph is worth that.

The rule that resolves it in the field

New Mexico's regulations do not ask what species you think it is. The booklet's test is blunt:

"Any trout with red slash marks below the jaw is considered a cutthroat."

A legal definition, not a field tip. If there is red under the jaw it counts as a cutthroat for regulatory purposes regardless of its genetics, and in most cutthroat water it is going back anyway.

When in doubt, it is a cutthroat.

For your challenge photo

A clean side view with the jaw visible. The slash is the whole submission. The three-quarter shot from above, which is what most people instinctively take, hides exactly the mark a reviewer needs. Fish in the water or just above it, camera ready before the fish comes up.

Range and status in New Mexico

Northern New Mexico headwater streams and some high lakes. NMDOW names three regions, the Rio Costilla, the upper Pecos and the Jemez, then points anglers at its own interactive fishing waters map. That map is the right place to get a specific water: it is current, and it comes with the rules attached.

• ~12 percent of historic range (USFWS and NMDOW, independently)
• 120+ conservation populations range-wide, 80+ in New Mexico
• 86 percent of populations in high wildfire-risk areas (2013 assessment)
• Not federally listed. Not warranted, 2014 and December 2024.

The headline number flatters the situation. The 12 percent measures stream length, not water volume or population health, and what it describes is a scatter of isolated headwaters, some holding only a few hundred fish, most genetically cut off from every other population.

Twelve percent of a range is not twelve percent of a fish.

The conservation story

Two things happened, in order. Heavy harvest in the settlement era thinned the native populations. Then, from 1896, the state stocked the water with fish from somewhere else (rainbows from the Northwest, brook trout from the southern Appalachians, brown trout from Europe), partly to replace what had been fished out.

Nobody understood what they were setting up. New Mexico's territorial game warden, reporting for 1909 to 1911, noticed the rainbows interbreeding with the natives and approved:

"These two varieties cross very readily, so that it is difficult now to find these distinct species… It has become a well-known fact to all students of fish life and culture, that crossing is beneficial."

The department's own magazine, looking back nearly a century later, delivered the verdict: that hybridization "reduced purebred populations of Rio Grande cutthroat to mere remnants in scattered headwaters."

Three mechanisms, genuinely different from each other.

Rainbow trout hybridize. Fertile offspring, rainbow traits dominant. A few generations of steady contact and the native fish is gone as a distinct thing without a single fish having been killed.

Brown trout outcompete. A New Mexico State University study of eight New Mexico streams found no evidence that brown trout prey on Rio Grande cutthroat at any life stage. They take the food. In streams without browns, prey flow to cutthroat measured 16 times what it was in shared streams.

Brook trout compete and prey. They take food and space, and unlike browns they eat cutthroat eggs and fry.

The work now. Five moves, repeated: remove nonnative fish from a stretch of historic habitat; build a barrier so they cannot swim back up; duplicate at-risk populations by transfer so a single fire cannot erase a lineage; propagate genetically pure fish at a hatchery; and do the unglamorous riparian work of livestock exclosures, willow planting and streambank stabilization.

In the Rio Costilla watershed alone, NMDOW describes more than 120 miles of stream and more than a dozen lakes restored. (Agency figures differ slightly between publications on the lake count, so a range is used rather than a number.)

The threats, in the order they will matter over the next decade.

Fire, and what follows it. The fire itself rarely kills the fish. What follows it does. Burned ground turns water-repellent, so the first hard rain runs off bare hillslopes instead of soaking in and bulks into a debris flow of sediment and charred material. USGS has measured post-fire runoff stripping dissolved oxygen out of rivers and killing fish, with the sedimentation that follows degrading habitat for years afterward. With 86 percent of populations in high-risk country, this is what could undo decades of work in one season.

Drought and warming water. Small headwater streams warm fast and shrink. In August 2026 a gauge in the upper Pecos at roughly 7,900 feet read 73.9°F, well past the point where releasing a fish stops being a kindness.

Continued contact with nonnative trout. The slow one, and the only one an angler personally affects.

Handling this fish, and when not to fish for it

Roughly eighty small, isolated populations hold everything that is left of New Mexico's state fish, and most of them are in country that burns. A fish that dies after release is not replaced from somewhere else.

There is no somewhere else.

When not to fish at all

Fish early. Water is coldest between dawn and mid-morning. Wyoming's guidance is to fish sunrise to noon and stop by midday on warm days.

How to handle it

Steps 1 through 8 are NMDOW's own published Catch and Release Tips, 2026–2027 rules booklet, p. 21. The agency's words, not ours.

1. Land the fish quickly and don't play it to exhaustion.
2. Use a landing net whenever possible.
3. Keep the fish in the water.
4. Do not squeeze or grab any part of the fish. Wet your hands first if you must handle the fish.
5. Gently remove the hook.
6. If the hook is swallowed deeply, cut the leader.
7. Let a tired fish recover. Hold it by the tail in the water, supported from below, until it swims away.
8. Never toss or throw a fish back into the water.

The law does not require the following. We are asking you to. Pinch your barbs. Keep air exposure to a few seconds; if you are holding the fish out of the water, hold your own breath, and when you want to breathe, so does the fish. Never lift a fish by the jaw or hold it vertically. Wet everything the fish touches, including the rock you are kneeling on.

The photograph problem

The challenge requires a photo of every fish, and much of the water this species lives in is catch-and-release by regulation. That tension is real and the program does not resolve it.

Have the camera ready before the fish is. Decide the shot in advance, phone out and unlocked, somewhere you can reach.

• Take the photo with the fish in the water or an inch above it. Over the net, over the water, never over rocks or a dry bank.
• One frame, maybe two. You need the jaw and the flank. That is one photograph.
• If the fish is struggling, put it back and take no photo. The cost is one species on a list with no deadline. Weigh that honestly against the alternative.
• If you drop it, you are done photographing. Revive and release.

And frame the fish, not the place. A recognizable landform behind a small headwater fish is a location disclosure that outlives your trip and travels further than you meant it to.

What the law requires

No special permit exists for this species. There is no cutthroat equivalent of the free Gila trout permit. A standard license and the usual validations and stamps apply, and stamps are required on Forest Service and Bureau of Land Management land, which covers most of the country this fish lives in.

This fish is not federally listed, and outside the Special Trout Waters it is legal to keep under a reduced limit. That surprises people, and it is true.

Catch-and-release is required by regulation in the Special Trout Waters and in the Native Trout Conservation waters, where the rule reads: "Catch-and-release only for Rio Grande cutthroat trout and Gila trout." Those waters also carry a tackle restriction (artificial fly or lure with a single, barbless hook), and it is not a suggestion.

The red-slash rule is a legal definition. "Any trout with red slash marks below the jaw is considered a cutthroat."

Chumming and baitfish are prohibited in every Special Trout Water, and it is illegal to disturb rocks, plants or sediment to attract fish.

There is no spawning protection of any kind. The word "redd" does not appear once in the 52-page rules booklet. Fishing in October for cutthroat puts you out during the brown trout spawn, on the same rivers. Clean, light-colored gravel at the tail of a pool or the head of a riffle is a redd. Walk around it. A single wading over a redd close to hatching killed up to 43 percent of the eggs and pre-emergent fry in a study that tested it directly, with similar effects for browns, rainbows and cutthroat.