All head and no swim bladder — which is not, on its own, the tell everyone thinks it is.
First checkIs the head clearly wider than the body behind it? That is a sculpin rather than a darter, which also has fan-shaped side fins. Then check for scales — there should not be any.
A sculpin is a head with a fish attached. Broad, flattened, frog-like, a mouth far too big for the body behind it, and a pair of pectoral fins so large that one state agency describes them sticking out from the sides like little feet, used to scoot across rock. It has no scales — prickles instead — and no swim bladder, so it stays on the bottom and moves in short quick dashes. Cold clear water, gravel to cobble, spring branches and riffles; and in Lake Superior, deep bottom, where a 1988 study found slimy and spoonhead sculpin most abundant between fifty and ninety metres.MDC-MOTTLED-SCULPIN, USGS-LKSUP-SCULPIN-BIOEvidence from: Depth figure: Lake Superior, 1988Dispute
Here is the useful correction, and it is one almost no fishing source makes. The famous sculpin fact — no swim bladder — does not separate a sculpin from a darter. Missouri's own field guide says the darter's swim bladder is absent or much reduced too, says darters sink to the bottom when they stop swimming, and describes the mottled sculpin moving in short, quick dashes in a manner similar to darters. If you are calling a sculpin because it sank, you may be holding a darter. Use the scales, the softness of the dorsal spines and the width of the head instead.MDC-DARTERS, MDC-MOTTLED-SCULPINDispute
One more piece of housekeeping. Sculpin get blamed for eating trout eggs, and they do eat fish eggs. But Missouri's field guide says sculpins do not feed to any great extent on trout eggs and young, and a southwest Montana study reported in Montana's field guide found bottom-dwelling aquatic insects made up 99.7 per cent of the diet. No consulted source makes a population-level claim, and this entry does not make one either.ADFG-SLIMY-SCULPIN, MDC-MOTTLED-SCULPIN, MTFG-ROCKY-MTN-SCULPINEvidence from: 99.7%: one southwest Montana studyDispute
The tell
What settles it, and what settles against it.
Read off this record's own diagnostic weights, heaviest first. A structure near the top of the left column does most of the work on its own; one near the bottom only leans.
Argues for Sculpin
Head wide and flattened, wider than the body behind it+8
Big fan-shaped side fins the fish props itself on+7
Fish-shaped forage silhouette (minnow / shiner / fry) — not an insect+6
Sits on the bottom and darts — it does not hover+6
Tail fin rounded or squared off, not forked+2
Spiny front dorsal fin, separate from or joined to a soft second dorsal (perch, sunfish)+1
Argues against it
No pelvic fins on the underside at all-5
Sawtooth belly — a row of sharp scutes along the midline you can feel-5
Small fleshy fin between the dorsal fin and the tail-5
Moving as a school or tight bait cluster, not as a single insect-4
One dorsal fin running most of the length of the back-4
Deep-bodied and strongly flattened side to side-4
Last dorsal ray drawn out into a long trailing thread-4
Rows of smaller spots trailing behind the shoulder spot-4
Dark opercular flap (ear flap) at the rear corner of the gill cover-4
Body translucent — light passes through it, and the backbone or gut shows-4
Body long and thin, many times longer than it is deep-3
Dark spot just behind the upper edge of the gill cover-3
Eye diameter greater than the length of the snout-3
Blunt, flattened head with a small mouth at the front-3
One soft dorsal fin only, with no spines (minnows, shads, herrings)-2
Mouth angled upward, the lower jaw leading-2
Dives into clean sand and disappears-1
Rounded, cigar-shaped body — not slab-sided-1
Snout overhangs the mouth, its tip in front of the jaw-1
A structure at −4 or below is treated as a hard exclusion by the comparison tool rather than as a penalty: if you saw it, this group is ruled out and no amount of matching elsewhere brings it back. Run a comparison →
Life stages
What it looks like, stage by stage.
Sculpin — First yeardrawn
First yearthe stage a fish meets
Size in handNot stated by the sources consultedDispute
What you see
The wide flat head is proportionally even more obvious than on an adultDispute
Mottled camouflage that matches whatever rock it is sitting onDispute
Where it turns up
Under and among rocks in clear cold gravel-and-cobble streams and spring branches.Dispute
Lateral line incomplete in slimy and mottled sculpin, stopping beneath the base of the second dorsalCTDEEP-SLIMY-SCULPIN, MDC-MOTTLED-SCULPINEvidence from: Slimy and mottled sculpinDispute
Where it turns up
On and under the bottom, wedged among rocks; also on deep lake bottom, where several species live as deepwater benthic prey fish.USGS-SCULPIN-SYNTHESISEvidence from: Laurentian Great LakesDispute
How it moves
Lies motionless then dashes; appears to hop, scooting on the pectorals. No swim bladder, so it stays on the bottom.MDC-MOTTLED-SCULPINDispute
Cues this stage offers the comparison
Head wide and flattened, wider than the body behind it
Big fan-shaped side fins the fish props itself on
Sits on the bottom and darts — it does not hover
Two dorsal fins with a clear gap between them
Fish-shaped forage silhouette (minnow / shiner / fry) — not an insect
Confused with
Telling it from what it isn't.
SculpinvsAquatic worms
A sculpin is a fish with fins and a hard head. If it has neither, you are looking at a worm.
Where in the column it mattersIn the substrate. There is no swim bladder, so there is no hovering. This animal is on the bottom or it is briefly between two parts of the bottom.
Read from the record's own position notes: on the bottom and under it — wedged among rocks, under cover, extremely cryptic.
Reference windows
When this group is typically available.
Typical published ranges only. Elevation, latitude, tailwater release and a given year's weather move all of these, often by weeks. This is never a statement about today.
1 reference window
Late-winter nest under rocksadult
JFMAMJJASOND
Sculpin nest under rocks in late winter to early summer, and the male guards the eggs; slimy sculpin in Alaska spawn in spring after the ice breaks up. The fish is in the same water all year; the seasonal event is the nest, not the animal appearing.
Observed: Months from Idaho (late winter to early summer), Missouri Ozarks (March to June, mottled sculpin) and Montana (May-June). Later in the far north. Tidewater sculpin are a different problem.
No reviewed dossier names this group. That is an absence in the dossier layer rather than a finding about the animal — four dossiers exist and only one of them names any forage group at all.
Nothing in the pattern layer is mapped to this group, so no presentation family follows from it here.
Not known
What this entry cannot tell you.
11 of them. The limits are part of what was reviewed rather than a disclaimer bolted on afterwards. An entry that hid them would be claiming more than it checked.
Written by the reviewer
Declared by the reviewerAbsence of a swim bladder does not separate sculpin from darters; the sources describe the darter's as absent or much reduced too.Dispute
Declared by the reviewerOne agency notes slimy sculpin are mistaken for young burbot and gives no separating characters. Neither does anything else consulted.Dispute
Declared by the reviewerThe most-repeated sculpin fact is the weakest separator. No swim bladder is true and well sourced, but a darter's is also described as absent or much reduced, so a sinking bottom fish is not automatically a sculpin. Scales, dorsal-spine stiffness and head width are the characters that actually work.MDC-DARTERS, MDC-MOTTLED-SCULPINDispute
Declared by the reviewerOne agency notes slimy sculpin are sometimes mistaken for young burbot and gives no separating characters. Neither does any other source consulted.ADFG-SLIMY-SCULPINDispute
Declared by the reviewerSize ceilings differ by source — about 4.5 inches for mottled sculpin, under five to six inches generally, usually under six inches. Compatible ranges, but no single number is offered.MDC-MOTTLED-SCULPIN, NPS-SCULPINS, IDFG-SCULPIN-WEDispute
Declared by the reviewerThe claim that sculpin suppress trout by eating trout eggs is not supported by the sources consulted. Missouri's field guide says sculpins do not feed to any great extent on trout eggs and young, and one southwest Montana study found bottom-dwelling aquatic insects made up 99.7 percent of the diet. No consulted source makes a population-level claim.MDC-MOTTLED-SCULPIN, MTFG-ROCKY-MTN-SCULPINEvidence from: 99.7% figure: one southwest Montana study of Rocky Mountain sculpinDispute
Sources disagreeThe National Park Service says sculpins' spines can pierce unwary hands, in a family-wide account weighted toward marine species; Missouri Department of Conservation describes the dorsal spines of its freshwater sculpins as soft and flexible, superficially like soft rays.
Sources disagreeSculpin spawning dates differ by source and species: Idaho Fish and Game says late winter to early summer; Missouri gives early March through April for mottled sculpin (to late June in the Ozarks); Montana gives May and June; Alaska says slimy sculpin spawn in spring after ice break-up.
Read off the record
Nobody typed these. They are fields that are empty, said out loud rather than left for you to notice from a section that simply is not there.
PatternsNo fly pattern in the pattern layer is mapped to this group. Whether anything imitates it is not answered here.
What eats itNo reviewed species dossier names this group. Some dossiers describe forage in class terms — small forage, insects, bait — and those are shown below, but a class description is not a reviewed link to this group and none is claimed.
Sources
Everything above rests on 13 published pages.
These are every page behind this entry. Where a reviewer traced a line above to the pages that carry it, that line names them itself, with where the evidence comes from when it is narrower than the whole entry. A line with no names beside it rests on this list as a whole: nobody has yet checked which page carried it, and naming one would be a mapping nobody made.
A plate shows shape. It cannot show a gill beating, a mask firing, or an animal reversing into sand — so where motion is the field mark, the entry points at motion. These are demonstrations, selected by hand and by publisher. Nothing here is a source: it changes no score, no window and no reviewed claim.
Tip of the Mitt Watershed Council. The look-alike that matters most here: a native sculpin against an invasive round goby, on the pelvic fins.
Public agency or non-profit · external video · title read back from the publisher 2026-09-09
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