First checkOne joined or barely divided dorsal fin on a very deep body, and no spines on the gill cover. That is a sunfish, not a perch.
A young sunfish is spiny-rayed like a perch, so the first cut puts them in the same half of the key. What separates them is the shape and the flap.Dispute
Sunfish are very deep — roughly half as deep as they are long — with the spiny and soft parts of the dorsal joined into one fin or only slightly divided, rather than standing apart. Adults carry a dark opercular flap, the ear flap, at the rear corner of the gill cover.MDDNR-BLUEGILL-BIOLOGY, CTDEEP-SUNFISHES, CTDEEP-BLUEGILLEvidence from: Ear flap: adultsDispute
They leave open water early. Fry are pelagic for a few weeks and then return to weed and cover, at twenty-one to twenty-five millimetres in the one Indiana lake where it was measured. Juveniles may still move into open water at night.WIDNR-BLUEGILL-LIT-REVIEWEvidence from: Crane Lake, Indiana; diel movement from Shoup et al. 2014Dispute
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 Sunfish, young of year
Fish-shaped forage silhouette (minnow / shiner / fry) — not an insect+6
Spiny front dorsal fin, separate from or joined to a soft second dorsal (perch, sunfish)+6
Dark opercular flap (ear flap) at the rear corner of the gill cover+5
Deep-bodied and strongly flattened side to side+5
Dark vertical bars down the flank, not a horizontal stripe+4
Moving as a school or tight bait cluster, not as a single insect+2
Argues against it
One soft dorsal fin only, with no spines (minnows, shads, herrings)-5
No pelvic fins on the underside at all-5
Sawtooth belly — a row of sharp scutes along the midline you can feel-4
Small fleshy fin between the dorsal fin and the tail-4
Last dorsal ray drawn out into a long trailing thread-4
Rounded, cigar-shaped body — not slab-sided-4
Body long and thin, many times longer than it is deep-4
One dorsal fin running most of the length of the back-4
Rows of smaller spots trailing behind the shoulder spot-4
Head wide and flattened, wider than the body behind it-4
Sits on the bottom and darts — it does not hover-4
Dives into clean sand and disappears-4
Blunt, flattened head with a small mouth at the front-3
Big fan-shaped side fins the fish props itself on-3
Dark spot just behind the upper edge of the gill cover-2
Two dorsal fins with a clear gap between them-2
Body translucent — light passes through it, and the backbone or gut shows-2
Snout overhangs the mouth, its tip in front of the jaw-2
Tail fin rounded or squared off, not forked-2
Eye diameter greater than the length of the snout-1
Mouth angled upward, the lower jaw leading-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 →
These groups name Sunfish, young of year in their own separators. If you arrived holding one of them and were not sure, this is the sentence that pointed you over.
Cisco / lake herringsaid
A spiny front dorsal fin on a very deep body is a young sunfish. Cisco has soft rays only.
Where in the column it mattersMid column. Fry are pelagic for several weeks, then return to weed and cover at around twenty-one to twenty-five millimetres and stay there. After that they are a cover animal, not an open-water one.
Read from the record's own position notes: fry stay pelagic for several weeks; then move to littoral vegetation at about 21 to 25 mm; warm quiet water with at least moderate vegetation.
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
Colonial nestingyoung-of-year
JFMAMJJASOND
Bluegill nest in colonies once the water reaches the high sixties. The fry move offshore for several weeks after swim-up, then return to weedy shallows for the rest of the summer. This is a nesting window, not a hatch.
Observed: Dated from Wisconsin and Iowa, with nesting months matching Connecticut. Maryland reports spawning from about 55 °F and into September.
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.
9 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 reviewerIn Iowa, first-year bluegill average roughly 25–50 mm; in one Indiana lake, fry returned from open water to cover at 21–25 mm.IOWA-DNR-FISHIOWA-BLUEGILL, WIDNR-BLUEGILL-LIT-REVIEWEvidence from: Iowa; Crane Lake, IndianaDispute
Declared by the reviewerThis entry covers Lepomis broadly. Separating bluegill from pumpkinseed or redear as young fish is not supported here.Dispute
Declared by the reviewerConnecticut DEEP compares the families directly on one character: sunfish lack the gill-cover spines perches carry. The rest of the separation is assembled from family characters.CTDEEP-SUNFISHESDispute
Declared by the reviewerIn Iowa, first-year bluegill average roughly 25 to 50 mm; in one Indiana lake (Crane Lake), fry returned from open water to weed cover at 21 to 25 mm.IOWA-DNR-FISHIOWA-BLUEGILL, WIDNR-BLUEGILL-LIT-REVIEWEvidence from: Iowa (first-year growth); Crane Lake, Indiana (Werner 1967, via WIDNR review)Dispute
Declared by the reviewerThis record covers Lepomis broadly; separating bluegill from pumpkinseed or redear as young fish is not supported here.Dispute
Declared by the reviewerConnecticut DEEP compares the two families directly on one character: sunfish lack the opercular spines perches carry. The rest of the young-sunfish versus young-perch separation is assembled from family characters, and no source describes the young fish side by side.CTDEEP-SUNFISHESDispute
Sources disagreeBluegill spawning temperatures differ by source and region: Wisconsin DNR's review gives an onset of 64 °F (Scott and Crossman) or 67 °F in Wisconsin, with little spawning below 70 °F in one set of lakes; Iowa gives 70 to 80 °F; Maryland DNR says spawning begins around 55 °F and may continue through September.
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 7 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.
Engbretson Underwater Photography. The deep slab-sided body turning edge-on to nothing and back to a full disc, and the dark ear flap flaring.
Working biologist · external video · title read back from the publisher 2026-09-09
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