Redband Rainbow Trout

What “Redband” Means

Redband trout are the interior forms of Oncorhynchus mykiss — the lineages that were cut off from the coastal rainbow trout of the Pacific slope and left to evolve in the arid interior. They are conventionally split into three groups: the Columbia River redband of the interior Columbia and Snake basins above the Cascade crest; the Great Basin or Oregon desert redband of the closed basins of south-central and southeastern Oregon and northern Nevada; and the Sacramento redband of the McCloud River drainage in northern California. What they share is a long history of isolation in water that is warmer, more variable and less reliable than anything coastal rainbows face.

The name refers to a broad brick-coloured lateral band, usually more saturated and more sharply defined than on a coastal rainbow, over a body that often keeps distinct parr marks into adulthood. Interior fish typically carry heavier, rounder spotting concentrated above the lateral line, white to orange tips on the pelvic and anal fins, and in some desert populations a strong yellow-orange cast to the belly and cheeks. These are tendencies rather than diagnostic characters, and hatchery rainbow introgression has blurred them in many drainages.

The Unsettled Name

The taxonomy is genuinely contested and has been for decades. Two subspecies names are in common use: Oncorhynchus mykiss gairdneri, generally applied to the Columbia Basin interior redband, and Oncorhynchus mykiss newberrii, generally applied to the Great Basin and Klamath forms. Neither application is universally accepted, the boundary between them is disputed, and some authors treat the desert and Klamath fish as distinct again from both.

Federal documents have handled this by declining to resolve it. In its 12-month finding on the petition to list the Great Basin redband trout, the U.S. Fish and Wildlife Service referred to the fish simply as Oncorhynchus mykiss ssp. and stated that for the purposes of the status review it assumed that trout classified by state agencies in the six basins as redband trout represented the Great Basin redband trout, “even though the precise genetic characteristics of those stocks may not be known” (USFWS 12-month finding, 2000). Recent peer-reviewed work on Klamath fish uses O. m. newberrii without qualification (Ortega et al. 2023), while Idaho and interior Columbia work commonly uses gairdneri. Both names are in current scientific use; neither is settled.

Genetics has complicated rather than simplified the picture. In the Upper Klamath Basin, analysis has identified distinct inland and coastal genetic lineages of O. mykiss occupying the same basin, a legacy of both natural history and a century of dam construction and stocking (Pearse et al. 2011), and isolated interior populations such as the Crane Prairie fish in the upper Deschutes have turned out to be genetically distinct from their neighbours (Matala et al. 2008).

Heat and Low Oxygen

The defining biological fact about interior and desert redband is that they tolerate conditions that would kill a coastal rainbow. The Fish and Wildlife Service put it directly: Great Basin redband trout “can withstand short periods of time at peak water temperatures of 24-27 deg. C (75-80 deg. F), which would be lethal to most other trout” (USFWS 2000). Laboratory work on three genetically distinct redband populations in southeastern Oregon measured critical thermal maxima of 29.4 ± 0.1 °C — about 85 °F — and documented rising metabolic costs and thermal sensitivity in larger fish between 24 and 28 °C (Rodnick et al. 2004).

That tolerance has a genetic and physiological basis rather than being mere acclimation. Genome scans comparing desert and montane redband found markers under selection associated with climate, and a pattern of isolation by temperature rather than by distance alone (Narum et al. 2010). Desert fish show measurably higher maximum heart rates and higher cardiac rate-limiting temperatures than montane fish from the same species (Chen et al. 2018), and whole-genome resequencing has linked thermal-stress performance to a small number of chromosomal regions, including a ceramide kinase gene implicated in cardiac performance under heat and low oxygen (Chen et al. 2020). Heat-stress transcriptomics show divergent expression responses between populations from different climates (Narum et al. 2015), and differential expression of respiration-control genes has been proposed as part of the mechanism (Garvin et al. 2015).

Low dissolved oxygen travels with high temperature — warm water holds less of it, and desert streams that heat also stagnate. The same cardiac and respiratory traits that buy heat tolerance appear to buy hypoxia tolerance with it, which is why redband persist in reaches that fail conventional salmonid habitat criteria on both axes at once.

Refugia: How the Klamath Fish Survive Summer

Tolerance is not the whole answer. Redband survive interior summers largely by moving, and the Upper Klamath Basin is the clearest documented case. Adfluvial redband there occupy Upper Klamath Lake through the productive spring and autumn, then abandon it in summer: the fish “occurred only in cool tributaries or springs (<20 °C) and avoided Upper Klamath Lake (>25 °C)” (Hahlbeck et al. 2022). The lake is warm, shallow and hypereutrophic, and in summer it is uninhabitable for a salmonid; the groundwater-fed springs and spring-fed tributaries that feed it stay cold year-round because their temperature is set by aquifer temperature rather than by air.

This is a strict dependency, not a preference. A basin can be productive on an annual average and still be survivable only because a small number of spring complexes hold cold water through August. It also carries costs. Trout crowded into summer refugia in the Upper Klamath showed a fourfold decline in lamprey wounds but a threefold increase in severe anchor worm infestation, while a downstream population without access to thermal refuge carried neither parasite (Ortega et al. 2023). Refuge habitat concentrates fish, and concentration has consequences.

Life History and Movement

Redband are unusually flexible about how they use a basin. Populations may be resident in a few miles of headwater stream, fluvial between a tributary and a mainstem, or adfluvial between a lake and its tributaries, and the same drainage often holds more than one form. Even after impoundment removed the migratory route, adfluvial Klamath redband have been shown to retain smoltification characteristics — the physiological machinery for migration persists after the migration itself has been blocked (Holecek et al. 2012). Spawning is a spring event, tied to declining flows and rising temperatures, generally between March and June and earlier at low desert elevations than at altitude.

Distribution within a desert basin tracks the intersection of temperature, flow permanence and cover rather than stream size, and occurrence and abundance differ systematically between desert and montane streams (Meyer et al. 2010). Condition indicators from field populations have been used to read thermal habitat quality directly from the fish (Kammerer and Heppell 2012).

Status and Threats

The Fish and Wildlife Service found in 2000 that listing the Great Basin redband trout as threatened or endangered was not warranted, across the Catlow, Fort Rock, Harney, Goose Lake, Warner and Chewaucan basins (USFWS 2000). That finding did not resolve the underlying vulnerabilities. Desert populations are small, isolated, and dependent on a limited number of thermally reliable reaches; the same isolation that produced their distinctiveness leaves them without recolonisation sources after a drought, a fire or a dewatering event.

Genetic dilution is the other persistent threat. Hatchery rainbow trout and nonnative cutthroat both hybridise with redband, and in the Boise River drainage interspecific hybridisation was detected at 14 of 41 sampled locations, though heavy introgression was concentrated in relatively few streams (Neville et al. 2011). Nonnative brook trout compete directly in Great Basin headwaters (Miller et al. 2013), and hybridisation status and summer movement remain an active research question in interior Columbia populations (Walser et al. 2025).

Redband as an Angling Fish

Redband are a small-water fish in most of their range. Desert stream populations mature at modest sizes and are dominated by fish of a few years, while adfluvial and fluvial populations with access to a lake or a productive mainstem grow substantially larger. They are opportunistic feeders in food-poor systems, which tends to make them responsive when they are found — the difficulty is finding them, because in mid-summer a long stretch of apparently reasonable stream may hold nothing and a hundred yards of spring-influenced water may hold everything.

Water temperature is the practical index of where the fish are. In interior and desert basins the useful reading is not whether the stream is cold but where the cold is: the tributary junctions, the spring seeps, the shaded canyon reaches and the deep pools that stratify. As mainstem temperatures rise through the 70s °F, redband contract toward those places and stay there, and handling stress on fish already operating near their thermal ceiling compounds quickly.