Trout & salmon · Freshwater
Arctic grayling
Thymallus arcticus
Native northern coldwater salmonid; remnant and reintroduced interior populations require geographic restraint.
Also called grayling.
- Flowing water
- Stillwater
- Ordinary target
- 4 of 4 overlays reviewed
- Reviewed 2026-08-27
Take this somewhere
This page is the record. The reading is what happens when you add water, a season and a temperature to it — that is where the families below get ranked against each other instead of just listed.
Those three links carry the fish and nothing else. No conditions were declared on this page, so none travel, and the link says so rather than sending an empty reading.
The half nobody publishes
What this record does not know
Everything else on this page comes from a named agency or peer-reviewed source. This is the other side of that: the questions a reviewer went looking for an answer to and came back without, and the fields the record leaves empty because filling them would mean guessing.
It is here rather than at the bottom because a page that only shows what it knows is easy to read as a page that knows everything. For Arctic grayling there are 22 of them.
Named by a reviewer
19Somebody looked for this and wrote down that they did not find it.
- Behaviour
Nobody has sourced:
- diel tendency is unresolved — no diel activity study for this species was reached, and the class is set to mixed rather than guessed
- no primary source found for cold-front / barometric response
- no primary source found for turbidity or clarity response
- no primary source found for water-level or flow-change response
- no primary source found for angling-pressure response
- predator avoidance and structural cover use are not described in the sources reached; fields omitted
- aggression beyond dominance-hierarchy position allocation is not documented here
- Identification
Nobody has sourced:
- no sourced description of juvenile appearance or parr marking was found, so juvenileAppearance is omitted
- no sourced sexual dimorphism outside spawning colour was found, so the field is omitted
- typical adult weight is genuinely unresolved; the field records the documented scaling instead of a fabricated average
- the informal regional-name list was not audited against a naming authority
- Forage
Nobody has sourced:
- the catalog includes larger_prey_fish for this species; the sources reached support only smolt-scale and small fish, so larger_prey_fish is not carried into primaryForage and needs a human decision
- the catalog includes crustaceans indirectly via zooplankton only; no separate crustacean diet record was sourced
- no quantitative diet composition study by season or region was reached
- ontogenetic diet shift and prey-size shift are not documented in the sources reached; fields omitted
- Season
Nobody has sourced:
- spring and fall entries are thin — the sources describe movement but not habitat class, depth, or forage detail for those windows
- no light-sensitivity material for any season, consistent with the unresolved diel class
- stillwater (adfluvial) seasonal habitat is only weakly separated from riverine habitat in the sources reached
- no sourced early_spring, early_summer, or late_summer material
Absent from the record
3No reviewer wrote a gap here. The field is simply empty, which is its own answer.
- Water temperature
No agency or peer-reviewed temperature band for Arctic grayling was found that a review would accept. The reading runs without one rather than borrowing a number from a related fish.
- Identification
No reviewed image. A photograph is only in this catalog when an agency or a named creator labelled the subject, and nobody has cleared one for this species yet.
- Population context
No regional population profile is registered. The species-level reading stands on its own; it does not silently become a local one.
Where the record puts it
Water and range
Flowing water
6 reviewed holding classes- Riffle-to-run transition
- Run
- Pool head
- Deep pool
- Seam
- Side channel
Stillwater
5 reviewed holding classes- Inlet
- Outlet
- Drop-off
- Basin
- Rocky shoreline
DepthOften upper-to-mid column while feeding on drift, but moves deeper when bright, pressured, warm, or wintering.
Moving waterFeeds efficiently where drifting food crosses moderate current; uses deeper, slower pools for seasonal refuge and wintering.
LightDaylight and broken-light surface feeding is common when insects are available; clear water increases the value of approach and distance.
Thermal band
Temperature
No reviewed temperature band
Nobody publishes a preferred or active temperature range for Arctic grayling that a review would accept. Borrowing one from a related fish would look like knowledge and behave like a guess, so the reading runs without it and says which parts of the answer that weakens.
How it uses water
Behaviour
Feeding fish occupy positions within dominance hierarchies rather than dispersing at random, so the group is structured by competition. Winter is the exception: reduced feeding and metabolism allow large congregations of otherwise competitive fish.
A drift feeder that holds a focal position and intercepts what the current delivers. Position choice follows the drift-foraging model — the fish balances a low-velocity holding spot against access to faster water that delivers prey, maximising net energy intake. Alongside that, sources describe grayling as generalists that take whatever is abundant, including eggs and small fish.
Unresolved. The sources reached document drift foraging as a position-holding, prey-interception mode but do not characterise a diel feeding rhythm for this species. Do not read a low-light or nocturnal bias into this record.
Seasonal activityStrongly migratory on an annual cycle. Fish move to spawning habitat just before and after spring breakup, redistribute to summer feeding areas, and from early fall move — typically downstream — toward overwintering areas. Individual annual movement ranges from under a kilometre to over 160 km. Summer is the voracious feeding season; winter feeding is minimal.
Temperature-driven behaviourAdult growth is optimal between about 4 and 15°C (39–59°F). Above roughly 15°C fish are stressed; above 20°C is lethal without a route to escape, and the thermal maximum sits around 20–25°C. Young-of-year and juveniles grow across a slightly warmer 10–20°C band, which is consistent with the observed size-by-elevation sorting.
Depth movementUnder winter ice, telemetered fish selected depths greater than 1 m and water with dissolved oxygen above 4.0 mg/L, staying in the upper water column of the deeper, better-oxygenated zones. Adults in a mountain watershed were associated with pool and boulder habitat.
Facing the currentHolds a focal position facing into flow and intercepts drift, choosing the position that trades holding cost against delivery rate rather than occupying the fastest water.
Open waterLake-dwelling (adfluvial) populations are common and rely heavily on zooplankton, in contrast with river populations that feed primarily on aquatic insects.
TerritoryForaging positions are allocated through dominance hierarchies, so the best drift-delivery lies are held by dominant fish. This is spacing and competition, not a catch claim.
Spawning (conservation context)Spring spawner. Fish migrate to spawning habitat just before and after breakup and broadcast eggs over gravel; the eggs sink and lodge between pebbles, with no redd construction and no parental care. Fry hatch about three weeks later and hold in quiet water. Spawning habitat, spawning movements, and any spawning-associated concentration are excluded from target guidance. Conservation context: the Montana fluvial population is ranked S1 — declining and facing threats to persistence — and is the last native fluvial population in the lower 48 states.
Where the general rule stops
- Juvenile and adult thermal preferences are not identical; the band here is an adult-oriented field synthesis.
- Many lower-48 populations are conservation-sensitive; geographic presence must be verified rather than inferred from habitat alone.
What it can eat
Forage
- Aquatic insects
- Emerging insects
- Terrestrial insects
- Zooplankton
- Small forage fish
- Eggs
Generalists whose core intake is drifting aquatic insects — blackflies, mayflies, stoneflies, and caddisflies are named specifically. Beyond that they take what is abundant: salmon eggs, salmon smolts and other small fish, and terrestrial insects. Lake populations rely heavily on zooplankton instead. Capacity is not a current hatch.
- Feeding style
- Opportunistic
- Feeding zone
- Mixed
Through the year
- Spring
- Spring is dominated by the movement to spawning habitat rather than by a described feeding pattern; no season-specific diet composition was sourced.
- Summer
- The heavy feeding season — described as voracious feeding on drifting aquatic insects, especially blackflies, mayflies, stoneflies, and caddisflies. Terrestrials, eggs, and small fish appear opportunistically. This is capacity, not a declared hatch.
- Fall
- Feeding continues while fish move toward overwintering areas; no season-specific diet composition was sourced beyond continued opportunism.
- Winter
- Feeding is minimal, and metabolism drops far enough that normally competitive fish tolerate close congregation.
By life stage
- Young of year
- Young-of-year hold low-elevation, warmer, flat-water habitat over silty sand; a sourced prey composition for this stage was not located.
- Adult
- Drifting aquatic insects as the base, with eggs, small fish, and terrestrials taken opportunistically. Lake-dwelling adults rely heavily on zooplankton.
SubstitutionsThe clearest documented substitution is habitat-driven: river populations feed primarily on aquatic insects while lake populations rely heavily on zooplankton. Egg and small-fish use appears where those are seasonally available. Substitution is system-specific.
Diet capacity is not proof that a hatch, egg drop, or baitfish event is occurring. Observed current forage still comes from a user observation or Hatch Match.
Through the year
Season
Winter
- Where they sit
- Overwintering water — low-velocity, deep enough, oxygenated, free of frazil ice, with cover from predators. Under ice, depths greater than 1 m in the better-oxygenated zones.
- Depth
- Selects water deeper than 1 m under ice, holding in the upper water column where dissolved oxygen exceeds 4.0 mg/L.
- Feeding
- Minimal feeding; metabolism drops and normally competitive fish tolerate close congregation.
- Temperature
- Well below the 4–15°C growth band. Adults tolerate hypoxia to a 24-hour LC50 near 0.75 mg/L dissolved oxygen at 1–3°C; juveniles are less tolerant at 1.50–1.96 mg/L, and stress behaviour appears at or below 4.0 mg/L.
What would count against it
- treating a winter congregation as a feeding opportunity
- assuming a summer drift-feeding posture applies under ice
Spring
- Where they sit
- Movement to spawning habitat just before and after breakup, then redistribution toward summer feeding water.
- Movement
- The most directed movement of the year; individual annual ranges run from under a kilometre to over 160 km.
What would count against it
- using spawning habitat or spawning movement as holding water
Spring spawner. Spawning habitat, spawning movement, and any spawning-associated concentration are excluded from target guidance. The Montana fluvial population carries an S1 rank.
Summer
- Where they sit
- Summer feeding water — riffle-to-run, run, pool head, seam, and side channel in rivers; drop-off, basin, inlet, and outlet in lakes. Adults associate with pool and boulder habitat; sub-adults spread across riffle, pool, and cascade-boulder habitat.
- Movement
- Sorted by size along the drainage: largest adults highest and coldest, juveniles lowest and warmest.
- Feeding
- The voracious feeding season.
- Forage
- Drifting aquatic insects — blackflies, mayflies, stoneflies, caddisflies — with terrestrials, eggs, and small fish taken opportunistically. Lake fish lean on zooplankton.
- Temperature
- Adult growth optimal 4–15°C (39–59°F); stress above about 15°C; lethal above 20°C without escape. Young-of-year and juveniles grow across 10–20°C.
- Current
- Holds a focal position that trades holding cost against drift delivery rate. Dominant fish hold the best-delivering positions.
What that changesDead drift and suspended drift match a fish intercepting what the current carries; swing and cross-current retrieve work the same delivery lanes. In lakes, horizontal retrieve and subsurface slow roll. Surface drift only when surface feeding is actually observed.
What would count against it
- inventing a hatch from diet capacity
- forcing water above about 15°C where cooler water is available
Fall
- Where they sit
- Feeding water giving way to a movement toward overwintering areas, typically downstream of the summer feeding water.
- Movement
- Slow migration toward overwintering habitat begins in early fall.
What that changesDead drift and suspended drift remain the reviewed flowing families while fish are still in feeding water.
What would count against it
- assuming summer feeding-area occupancy persists once the downstream shift begins
Spawning · Early spring, Spring
Spring spawner in shallow gravel-and-rock tributary or river habitat as cold water begins warming; timing is latitude- and elevation-sensitive.
Recorded as conservation context. No spawning site, staging concentration or migration bottleneck is named anywhere in this catalog, because naming one is how a population gets fished out.
Telling it apart
Identification
What to look at
- A very large sail-like dorsal fin with a scalloped edge — the single unambiguous field character.
- The dorsal fin is typically fringed in red and dotted with large iridescent red, aqua, or purple spots; the markings are most developed on large fish.
- Small black spots are scattered on the anterior sides, forward of mid-body — not a full-body trout spotting pattern.
- Pelvic fins carry iridescent orange, red, or pink stripes running along the rays.
- A black slash marks each side of the lower jaw.
- The iris is gold, and a gold band borders the white belly.
- Sides may run black, silver, gold, or blue depending on the population.
- Average adult length
- Sexual maturity is reached at roughly 10–12 in (255–305 mm), so most adults in a population sit at or above that. Exceptional fish reach about 20 in.
- Common angling size
- Around and somewhat above the 10–12 in maturity size in most populations; a defensible population-specific mean was not located.
- Typical weight
- Not well characterised as a single figure in the sources reached. Documented weights scale from roughly 3 lb at about 20 in to 5 lb 1 oz at the 24 in maximum; a fish over 3 lb is treated as a trophy by the Alaska agency programme.
- Maximum documented
- 610 mm (24 in) and 2.3 kg (5 lb 1 oz); an Alaska state record of 23 in and 4 lb 13 oz is also reported.
- Longevity
- Up to 30–32 years in Alaska. Life span is strongly population-dependent — the Montana fluvial population rarely lives beyond 5 years, with spawning dominated by age 3–4 fish. First spawning occurs between ages 4 and 7 in Alaska and by age 3 in Montana.
What it gets confused with
- Mountain whitefish
- Whitefish has a short 12–13 ray dorsal with no markings, no body spots at all, and a small mouth set under a blunt overhanging snout. Grayling has the sail dorsal with coloured spots and a terminal mouth.
- Trout and char
- Trout and char carry a normal, small dorsal fin and spotting distributed over the body and often the tail. No trout or char has the scalloped sail dorsal or the striped pelvic fins.
- Ciscoes and other coregonines
- Ciscoes are slender, herring-like, and plainly silver with a short dorsal fin. They lack both the sail dorsal and the black lower-jaw slash.
What follows from all of that
Presentation families
Flowing water
Dead drift
Allow a food-form imitation to move at or near current speed through a defined feeding lane.
- controlled depth
- minimal drag
- short-to-medium presentation lane
- occasional repositioning
What it asks of the tackle
- Depth control
- High
- Sensitivity
- High
- Casting distance
- Short to moderate
- Weight range
- 1/64–1/8 oz or unweighted fly
- Cover resistance
- Low
- Line visibility
- Low
- Retie frequency
- Moderate
Surface drift
Present a floating food form in a feeding lane with as little drag as the water allows.
- slack management
- reach or mend
- dead or micro-twitch
- leave it in the lane
What it asks of the tackle
- Depth control
- Surface
- Sensitivity
- Moderate
- Casting distance
- Short to moderate
- Weight range
- Unweighted
- Cover resistance
- Low
- Line visibility
- Low
- Retie frequency
- Moderate
Tight-line drift
Keep a near-direct connection to a drifting imitation so depth and contact can be felt without a floating indicator.
- in-touch leader
- lead the drift
- detect ticks and pauses
- reset after each lane
What it asks of the tackle
- Depth control
- High
- Sensitivity
- High
- Casting distance
- Short
- Weight range
- 1/64–3/16 oz
- Cover resistance
- Moderate
- Line visibility
- Low
- Retie frequency
- High
Swing
Let current carry a bait or fly across a lane so it broadens and lifts at the hang.
- downstream quartering
- controlled belly
- hang-down pause
- slow lift
What it asks of the tackle
- Depth control
- Moderate
- Sensitivity
- Moderate
- Casting distance
- Moderate
- Weight range
- Unweighted to 1/4 oz
- Cover resistance
- Low
- Line visibility
- Moderate
- Retie frequency
- Low
Stillwater
Horizontal retrieve
Move a swimming bait through a chosen depth band along structure or open water.
- count down
- steady or pulsing retrieve
- keep the band
- cover the edge
What it asks of the tackle
- Depth control
- Moderate
- Sensitivity
- Moderate
- Casting distance
- Moderate to long
- Weight range
- 1/8–1/2 oz
- Cover resistance
- Moderate
- Line visibility
- Low
- Retie frequency
- Low
Drop presentation
Let a bait fall on a controlled line into cover, along a wall, or through a hole in vegetation.
- place then fall
- watch the line
- hold at depth
- short hop only after the fall
What it asks of the tackle
- Depth control
- High
- Sensitivity
- High
- Casting distance
- Short
- Weight range
- 1/16–3/8 oz
- Cover resistance
- High
- Line visibility
- Low
- Retie frequency
- High
Surface retrieve
Work a floating bait across shade, weed edges, or low-light shallows.
- walk, pop, or crawl
- pause in holes
- keep it on top
- cover the edge
What it asks of the tackle
- Depth control
- Surface
- Sensitivity
- Low
- Casting distance
- Moderate
- Weight range
- 1/4–3/4 oz
- Cover resistance
- Moderate
- Line visibility
- Moderate
- Retie frequency
- Low
Suspend / pause
Leave a neutrally buoyant bait hanging in place where fish are already holding.
- reach the band
- long pause
- tiny pulse only if needed
- do not leave the zone
What it asks of the tackle
- Depth control
- High
- Sensitivity
- High
- Casting distance
- Moderate
- Weight range
- 1/8–3/8 oz suspending
- Cover resistance
- Low
- Line visibility
- Low
- Retie frequency
- Low
What moves them for this fish
Reviewed rules that push particular families up when the conditions match. Each one names the conditions it needs and why it exists, so you can disagree with it.
Verified insect input is a strong grayling-specific reason to favor surface/drift mechanics when those families are reviewed for the declared water type.
When
Summer or Late summer · Emerging insects, Terrestrial insects, Aquatic insects
Moves up
Surface drift, Dead drift, Tight-line drift, Surface retrieve
Reviewed 2026-08-27
Cold grayling refuge behavior is more depth-oriented than their warm-season surface identity.
When
cold refuge · Deep pool, Basin, Drop-off
Moves up
Dead drift, Tight-line drift, Drop presentation, Suspend / pause, Surface drift, Surface retrieve
Reviewed 2026-08-27
Where every sentence came from
Sources
Agency
Alaska Department of Fish and Game — Arctic Grayling species profile
Used for identification; behaviour; forage; season. Read 2026-08-30, next check 2026-12-08.
Agency
Alaska Department of Fish and Game — Arctic Grayling (Wildlife Notebook Series)
Used for identification; behaviour; forage; season. Read 2026-08-30, next check 2026-12-08.
Agency
Used for identification; behaviour; forage. Read 2026-08-30, next check 2026-12-08.
Agency
Used for behaviour; season. Read 2026-08-30, next check 2026-11-23.
Agency
Alaska Department of Fish and Game Arctic grayling species profile
Used for habitat, thermal band and presentation families. Read 2026-08-27, next check 2026-11-27.
Agency
USGS Arctic Grayling species profile
Used for habitat, thermal band and presentation families. Read 2026-08-27, next check 2026-11-27.
Peer reviewed
Used for behaviour; forage; season. Read 2026-08-30, next check 2026-11-23.
Peer reviewed
Used for behaviour; season. Read 2026-08-30, next check 2026-11-23.
Peer reviewed
Recent peer-reviewed Arctic grayling thermal ecology literature
Used for habitat, thermal band and presentation families. Read 2026-08-27, next check 2026-11-27.
Peer reviewed
Used for behaviour. Read 2026-08-30, next check 2026-11-23.
A source with no link predates the rule that one has to carry a URL. It is still a real citation and still checkable; it just takes a search rather than a click, and that is worth knowing before you rely on it.