First checkIs the eye wider than the snout is long, with no thread on the back fin? That is alewife rather than shad.
Alewife is the herring you meet without the thread. Same deep slab-sided silver body as shad, same sawtooth belly — sharper, in fact, than most of the family — but the back fin ends cleanly and the eye is conspicuously large.Dispute
The eye is the field character worth learning: its diameter is greater than the length of the snout. That ratio also separates it from blueback and skipjack herring, whose eyes are no wider than the snout is long. One old name for the fish is bigeye herring.NY-SEAGRANT-INVASIVE-HERRING, ADW-ALEWIFEDispute
Where they sit in the water changes with the season in a way that matters. In the Great Lakes: open water most of the year, near the bottom in winter and early spring — because in a cold lake the warmest water is the deepest.USGS-GLSC-LAKE-ONTARIO-PREYFISHEvidence from: Lake Ontario / Great LakesDispute
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 Alewife / river herring
Fish-shaped forage silhouette (minnow / shiner / fry) — not an insect+6
Sawtooth belly — a row of sharp scutes along the midline you can feel+6
Moving as a school or tight bait cluster, not as a single insect+5
Dark spot just behind the upper edge of the gill cover+4
Deep-bodied and strongly flattened side to side+4
Eye diameter greater than the length of the snout+4
One soft dorsal fin only, with no spines (minnows, shads, herrings)+3
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
Small fleshy fin between the dorsal fin and the tail-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
Rounded, cigar-shaped body — not slab-sided-3
Blunt, flattened head with a small mouth at the front-3
Big fan-shaped side fins the fish props itself on-3
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
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 Alewife / river herring in their own separators. If you arrived holding one of them and were not sure, this is the sentence that pointed you over.
Sunfish, young of yearsaid
A sawtooth belly and a big eye on a soft-rayed fish is alewife. Sunfish is spiny and smooth-bellied.
This is the hard one and it is not settled by the spot. Alewife has a shoulder spot AND belly scutes. Look for the trailing rows of smaller spots, and for menhaden's much larger head — about a third of the body without the tail.
Where in the column it mattersMid column. Open water for most of the year and hard on the bottom in winter and early spring, because the warmest water in a cold lake is the deepest. Young-of-year fish stay above the thermocline by day while the adults are below it.
Read from the record's own position notes: open water for most of the year; near the lake bottom in winter and early spring; young-of-year fish stay above the thermocline by day; runs into tributaries and shallow water 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.
2 reference windows
Spawning runadult
JFMAMJJASOND
Sea-run adults leave salt water and run up into lakes and ponds to spawn. Landlocked alewife, including the Great Lakes fish, live in fresh water all year, and sea-run young stay in fresh water until summer or autumn.
Observed: Dated from Maine. Run timing shifts strongly with latitude and this window is not continental.
The year's young drop back down through the second half of the season at roughly 32–152 mm — which is the size range that matters to anything hunting them.
Observed: Dated from Maine sea-run populations. Landlocked alewife, including the Great Lakes fish, do not go to sea.
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.
Written by the reviewer
Declared by the reviewerLandlocked Great Lakes alewife are much smaller than the anadromous Atlantic form; the sizes here follow Great Lakes survey figures.USGS-NAS-ALEWIFEDispute
Declared by the reviewerThe 100 mm cutoff separating age-0 from older fish is a Lake Michigan survey convention, not a biological boundary.USGS-GLSC-LAKE-MICHIGAN-PREYFISHEvidence from: Lake MichiganDispute
Declared by the reviewerBlueback herring is separated reliably by the colour of the body-cavity lining; on a live fish, its smaller eye — no wider than the snout is long — is the hint.USGS-NAS-ALEWIFE, NY-SEAGRANT-INVASIVE-HERRINGDispute
Declared by the reviewerLandlocked Great Lakes alewife run much smaller than the anadromous Atlantic form; the size bands here follow Great Lakes and survey figures.USGS-NAS-ALEWIFEEvidence from: Inland vs marine populationsDispute
Declared by the reviewerThe 100 mm total-length figure separating age-0 from older fish is a Lake Michigan survey convention, not a hard biological boundary.USGS-GLSC-LAKE-MICHIGAN-PREYFISHEvidence from: Lake Michigan fall bottom-trawl and acoustic surveysDispute
Declared by the reviewerThis record does not claim alewife are present in any particular water.Dispute
Sources disagreeMaine Department of Marine Resources gives two spawning temperature ranges on two pages: 12.8 to 15.5 °C on its river herring fact sheet, and from about 13 °C up to about 20 °C on its alewife page. The calendar window keeps the fact-sheet range.
Sources disagreeFamily placement differs by source: Maine Department of Marine Resources lists alewife in Clupeidae, while Missouri Department of Conservation places Alosa species in Alosidae after a 2022 split.
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 12 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.
SmithsonianSERC. A river herring run from underwater — how the fish hold, stack and move in a stream rather than how one looks in profile.
Research institute · external video · title read back from the publisher 2026-09-09
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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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