Round Whitefish

Identification

Round whitefish is a small salmonid built like a length of pipe. The body is slender, elongate and almost circular in cross section — the trait that gives the fish its name — with a short head, a blunt overhanging snout and a small, ventral, essentially toothless mouth set well back under the head. Colour runs olive to dark brown on the back, shading through silver sides to a white belly, with amber or pale orange pectoral and pelvic fins. Like every salmonid it carries an adipose fin. Juveniles wear two or three rows of dark spots along the flank that are easy to mistake for parr marks, and these fade with age. FishBase gives 11–15 dorsal soft rays and 10–13 anal soft rays.

The genus matters here. Round whitefish is a Prosopium, not a Coregonus, and the cleanest field character is the nose. Prosopium has a single flap of skin between the nostril openings on each side; the Coregonus whitefishes and ciscoes have two. The Alaska Department of Fish and Game’s account of the other Alaskan Prosopium, pygmy whitefish, lists that single internarial flap as a defining trait and notes the two Alaskan Prosopium are similar in appearance to one another. New York’s Department of Environmental Conservation makes the same point from the other end of the range, describing the single flap as the character “distinguishing it from other whitefishes.” Beyond the nostrils, the round body and small inferior mouth separate it from the deeper-bodied Coregonus whitefishes such as humpback whitefish, which develops a pronounced hump behind the head.

Separating round whitefish from mountain whitefish (Prosopium williamsoni) is a different problem, and one worth being blunt about: on external characters it is genuinely hard. The two congeners overlap almost exactly in the counts most often quoted — FishBase gives mountain whitefish 11–15 dorsal and 10–13 anal soft rays, identical to round whitefish — and both are slender, cylindrical, small-mouthed and silver. In practice the reliable discriminator is geography. Mountain whitefish ranges from the Mackenzie River drainage in the Northwest Territories south through western Canada and the northwestern United States to Nevada and Utah. It does not reach Alaska; it is absent from ADF&G’s list of Alaska fishes. A Prosopium in an Alaskan river is a round whitefish or, in a handful of southwestern and southcentral drainages, a pygmy whitefish.

Taxonomy and naming

Coregonine taxonomy is a mess, and round whitefish sits inside the mess rather than beside it. The species was described in 1784 by Pennant, working from Pallas, as Salmo cylindraceus — and the type material came from Siberia, from the Lena, Indigirka and Kolyma rivers, not North America. Eschmeyer’s Catalog of Fishes treats the name as valid in Prosopium and folds in a long list of junior synonyms including Coregonus quadrilateralis Richardson 1823, Prosopium quadrilaterale minor Koelz 1931, Coregonus preblei Harper & Nichols 1919, Salmo microstomus Pallas 1814 and Coregonus mongolicus Warpachowski 1900. Older North American literature refers to this fish as Coregonus quadrilateralis, and that name still turns up in historical records. Whether the North American and Siberian populations are one species is a question the synonymy papers over rather than settles.

Placement above the genus is also unsettled. ITIS (TSN 162008) and Eschmeyer’s both place Prosopium in family Salmonidae, subfamily Coregoninae, and that is the arrangement used here; other authorities have treated Coregonidae as a family in its own right. Common names are worse. A 2026 compilation of two centuries of Great Lakes coregonine records found that “every region, culture, and decade tended to carry with it a suite of new and different common names,” documenting roughly 140 additional regional names for the group beyond accepted nomenclature. Round whitefish alone answers to Menominee, frostfish and pilotfish depending on where you are standing.

Range and distribution

Round whitefish is a northern fish with a discontinuous North American distribution. It occupies Arctic and Pacific drainages from western Hudson Bay across to Alaska and northern British Columbia, and Atlantic drainages from Quebec and Ontario south to Connecticut, including the St. Lawrence and the Great Lakes basin — all the Great Lakes except Lake Erie. It also occurs widely in Siberian rivers. The documented latitude band is roughly 41°N to 72°N.

In interior Alaska the species is resident in clear upland streams of the Tanana drainage, including the Chena and Salcha rivers. Two ADF&G management reports carry the weight of that statement, and it is worth being precise about what each one does and does not say. Parker and Viavant’s Fishery Management Report No. 00-6 describes the Chena as “a clear to slightly tannic-stained stream containing resident populations of Arctic grayling and whitefish throughout its length, and of northern pike and burbot in its lower reaches” — resident whitefish along the entire river, but without naming the species. Gryska and Baker’s 2025 Fishery Management Report No. 25-33 for the Tanana Management Area names the whitefishes anglers actually catch: “least cisco Coregonus sardinella, humpback whitefish C. pidschian, broad whitefish C. nasus, and round whitefish Prosopium cylindraceum are caught occasionally by sport anglers.” Taken together with the absence of mountain whitefish from Alaska, round whitefish is the Prosopium in these rivers. That is an inference across two documents, not a single sentence in one of them.

Habitat and water temperature

Round whitefish is a benthic fish of cold, clear, well-oxygenated water — shallow margins of lakes and the gravel and cobble reaches of clear streams. FishBase records it from 4 to 72 m depth, usually shallower than 37 m, and gives a documented occurrence temperature range of 2–18°C (36–64°F). New York’s status assessment describes the habitat as deep, cold lakes with well-oxygenated deep zones, and states flatly that habitat specifics and vulnerability patterns for the species remain unstudied.

Hard thermal numbers are scarce. The best available measurement comes from a 2023 laboratory study by Harman and colleagues in Conservation Physiology, which reared round whitefish from eggs at 0.5, 2 and 6°C and then measured the temperature preference of the juveniles at 12 months. Preferred temperatures fell between 13.39 ± 0.99°C and 14.27 ± 0.95°C — roughly 56–58°F — with fish incubated coldest preferring the warmest water. That study also concluded round whitefish “appear more sensitive to elevations in rearing temperature than” lake whitefish.

On the egg side, Graham et al. (2016) put the optimal development temperature for round whitefish embryos at approximately 4.5°C (40°F) and note that mortality and deformity rates increase significantly when eggs are incubated warmer. That is a narrow window for a fish whose spawning gravel sits under ice for months.

No upper incipient lethal temperature has been published for round whitefish. The species has never had the thermal-tolerance workup routinely applied to trout and salmon. Anyone reading a live water temperature against this fish should treat about 54–59°F as the band it selects when given a choice, 64°F as the top of what has actually been recorded, and everything above that as unmeasured rather than known-safe.

Life history

Round whitefish spawn in late fall. New York DEC gives November to December over gravel shoals of lakes or at river mouths; Graham et al. record early November to early December in shallow near-shore water 2–8 m deep over rock-cobble substrate. Fish move inshore and upstream to spawn and swim in pairs; eggs are broadcast over the substrate and are not guarded. Incubation is long — New York puts hatching at approximately 140 days after spawning, which under ice means fry emerging in spring.

Growth is unhurried. New York reports young reaching 3–4.5 inches by the end of the first year and maturity at about 12 inches at age 3–4, with adults rarely exceeding 13 years. FishBase gives maturity near 30 cm and a maximum age of 16 years. Maine’s Department of Inland Fisheries and Wildlife reports a shorter working lifespan there, with eight years common. FishBase classes the species’ resilience as low, with a population doubling time of 4.5–14 years — a slow-turnover fish, which matters for how quickly a depleted population can recover.

Diet

Round whitefish is a bottom feeder with a small, downward-facing, toothless mouth, and its diet reflects that. New York lists mayfly larvae, chironomid larvae, small molluscs, crustaceans, fish and fish eggs. Maine reports a narrower menu — “almost primarily zooplankton and midge larvae, some crustaceans.” FishBase summarises adults as feeding on benthic invertebrates, fish and eggs. The egg-eating habit is consistent across accounts and is the one dietary trait with obvious relevance in salmon rivers, where drifting eggs are a seasonal food source.

Angling

Round whitefish is almost never a target. In the Tanana drainage, ADF&G’s 2025 management report groups it with the species “caught occasionally by sport anglers” — incidental to the Arctic grayling fishery that dominates the Chena and Salcha. Maine is more direct still: round whitefish are “rarely caught by anglers” because of their small mouths and invertebrate diet, and “very occasionally, smelt anglers in northern Maine will catch one incidentally.”

What catches do happen are a by-product of the fish’s biology rather than any particular technique. A small inferior mouth and a diet of chironomids, mayfly larvae and eggs means round whitefish come to hand mostly on very small subsurface offerings fished on or near the bottom, in the same clear cold gravel reaches that hold grayling. Where the fish shares water with spawning salmon, its documented appetite for eggs makes it an occasional incidental catch in that context too. There is no meaningful sport-fishery literature for the species anywhere in its range; ADF&G does not even maintain a species profile page for it, while it does for broad, humpback and pygmy whitefish. That absence is itself the most accurate summary of the fish’s angling profile.

Conservation

Globally the species is secure. NatureServe ranks it G5, FishBase records an IUCN assessment of Least Concern from September 2020, and it carries no United States federal listing — the U.S. Fish and Wildlife Service species profile exists but contains no listing action. North American abundance and distribution are both assessed as stable.

The picture at the southern edge of the range is very different. New York lists round whitefish as Endangered, with a state rank of S1S2 and Species of Greatest Conservation Need designation. The state’s status assessment documents a collapse from 68 Adirondack waters across 7 of 18 watersheds before 1977 to 8 waters across 5 watersheds since. DEC’s species account puts the historical figure at roughly 60 lakes including Big Tupper, Piseco, Raquette, Blue Mountain and the Fulton Chain, and records surveys from 1985–1987 finding the fish in only six Adirondack water bodies. The causes named are predation on eggs and fry by introduced yellow perch, predation by smallmouth bass, competition with lake whitefish and rainbow smelt, lost and silted spawning sites, and lake acidification. New York classes the species as extremely vulnerable to climate change, and management aims at securing self-sustaining populations in at least five Adirondack lakes, potentially with artificial propagation.

The Great Lakes are not reassuring either. Graham et al. note that round whitefish have “drastically declined in Lake Huron in recent years” and call for large-scale genetic work to support management, observing that the species “presented essentially a complete unknown in terms of a priori expectations about population structure.” Maine reports the same information gap in plainer language: “We have very little information on current round whitefish distribution, population status, and population trends.”

That is the honest position across most of the range. A cold-adapted, slow-growing, fall-spawning fish with a 4.5°C egg-development optimum, no published lethal thermal limit, no sport-fishery data and thin population monitoring is a species we would not notice losing quickly. In Alaska it appears secure and widespread. Elsewhere, the record is mostly absence of record.