First checkIs there a small fleshy fin between the back fin and the tail? That is an adipose fin. A cisco has no teeth; a rainbow smelt, which also carries the fin, has obvious teeth on the jaws and tongue.
The name is misleading and the body settles it. Cisco is a member of the trout and salmon family, and it carries the family's badge: a small fleshy adipose fin between the back fin and the tail. The look-alike that shares that fin is the rainbow smelt, not a herring.ILDNR-CISCO, DFO-BAITFISH-PRIMER, MANITOBA-BAITFISH-GUIDEDispute
The second difference is shape. Shad and alewife are deep and flattened side to side. A cisco is elongate and nearly round in cross section — you can feel it in the hand before you have looked at a single fin.Dispute
It is a cold-water, open-water animal that uses the full range of depths through the year, which is most of what governs where and when you meet it.USFWS-CISCO, MNFI-CISCO-ABSTRACTDispute
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 Cisco / lake herring
Fish-shaped forage silhouette (minnow / shiner / fry) — not an insect+6
Small fleshy fin between the dorsal fin and the tail+6
Rounded, cigar-shaped body — not slab-sided+5
Moving as a school or tight bait cluster, not as a single insect+4
One soft dorsal fin only, with no spines (minnows, shads, herrings)+2
Argues against it
Spiny front dorsal fin, separate from or joined to a soft second dorsal (perch, sunfish)-5
No pelvic fins on the underside at all-5
Sawtooth belly — a row of sharp scutes along the midline you can feel-4
Last dorsal ray drawn out into a long trailing thread-4
Dark vertical bars down the flank, not a horizontal stripe-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
Two dorsal fins with a clear gap between them-4
Rows of smaller spots trailing behind the shoulder spot-4
Tail fin rounded or squared off, not forked-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
Dark opercular flap (ear flap) at the rear corner of the gill cover-3
Deep-bodied and strongly flattened side to side-3
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
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
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 →
Adipose fin between the dorsal fin and the tailDispute
Elongate body, nearly round in cross sectionDispute
Silvery with a deep blue-green back; fins nearly clear, tail and dorsal tips darkUSFWS-CISCODispute
Where it turns up
Midwater in deep lakes for much of the year; shallow over rocky shoals to spawn, and in surface waters in winter and spring.USFWS-CISCO, MNFI-CISCO-ABSTRACTDispute
These groups name Cisco / lake herring in their own separators. If you arrived holding one of them and were not sure, this is the sentence that pointed you over.
Shiners and minnowssaid
An adipose fin before the tail points to a cisco or other salmonid, or to a smelt — not to a minnow.
Where in the column it mattersMid column. A pelagic animal: midwater in deep lakes, across a wide depth range, coming shallow over rock only to spawn.
Read from the record's own position notes: pelagic — open water, midwater in large and deep inland lakes; moves shallow over rock to spawn.
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-autumn spawningadult
JFMAMJJASOND
Cisco move off deep water onto shallow rocky shoals to spawn once the water drops below about 43 °F, with spawning peaking below about 39 °F.
Observed: Dated from Chaumont Bay, Lake Ontario. A separate spring migration exists in some waters and is not this.
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.
10 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.
Declared by the reviewerNo source consulted stated a young-of-year size, so none is given.Dispute
Declared by the reviewerCisco need cold water, and inland lakes at least 10 m deep. This entry describes the animal, not whether your water holds it.MNFI-CISCO-ABSTRACT, ILDNR-CISCOEvidence from: Michigan inland lakesDispute
Declared by the reviewerCisco need cold water, and inland lakes at least 10 m deep; this record is about what the animal looks like, not about whether your water holds them.MNFI-CISCO-ABSTRACT, ILDNR-CISCOEvidence from: Inland-lake depth figure is from MichiganDispute
Declared by the reviewerSources conflict on jaw position, and gill-raker counts (44 to 52 in one Michigan account) need a fish in hand, so neither is offered as a field character.MNFI-CISCO-ABSTRACT, MNDNR-CISCO-WHITEFISH-IDDispute
Declared by the reviewerNo young-of-year size is given because no source consulted stated one.Dispute
Sources disagreeJaw position is described both ways. Michigan Natural Features Inventory says the cisco's lower jaw is equal to or shorter than the upper jaw; Minnesota DNR says it extends up to or beyond the tip of the snout.
Sources disagreeIllinois DNR calls cisco a fish of shallow water; USFWS and Michigan Natural Features Inventory describe a pelagic cold-water lake fish that uses the full depth range of the Great Lakes and, inland, needs lakes at least 10 m deep.
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 8 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.
Declared gap. Credible material is conference talks and restoration webinars with no footage of the fish; everything showing a cisco is an ice-fishing catch video.
Carry it on
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Which fish in this kind of water are documented eating this class of forage, and how they behave when they are.
What this forage class asks of the setup — the weight it wants, and where the chain gives first.
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