First checkIs there a long thread trailing off the back fin? That is the one character in this group that nothing else shares.
A deep, slab-sided, silver fish in a school near the surface is a common big-water forage sight. Two animals here fit that description before you look closer: shad and alewife. Cisco, the other silver schooling fish, is long and slender instead.MDC-GIZZARD-SHAD, MAINE-DMR-ALEWIFE, ILDNR-CISCODispute
Shad settle it with one structure nothing else here has. The last ray of the back fin is drawn out into a long trailing thread. If you can see that thread, you are done.Dispute
The second check is the belly. Run a finger forward along the midline and shad and alewife both feel like a saw; a minnow and a cisco do not. Keel plus thread is shad. Keel without thread, with a big eye, is alewife.Dispute
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 Shad (gizzard and threadfin)
Fish-shaped forage silhouette (minnow / shiner / fry) — not an insect+6
Last dorsal ray drawn out into a long trailing thread+6
Moving as a school or tight bait cluster, not as a single insect+5
Sawtooth belly — a row of sharp scutes along the midline you can feel+5
Deep-bodied and strongly flattened side to side+4
One soft dorsal fin only, with no spines (minnows, shads, herrings)+3
Dark spot just behind the upper edge of the gill cover+3
Snout overhangs the mouth, its tip in front of the jaw+2
Blunt, flattened head with a small mouth at the front+1
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
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
Big fan-shaped side fins the fish props itself on-3
Body translucent — light passes through it, and the backbone or gut shows-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 →
Where in the column it mattersJust under the surface. Shad are met at or near the surface in constantly moving schools, and the same schools skitter across the top when something is pushing them. That surface behaviour is the observation, not a claim that they never go deep.
Read from the record's own position notes: near surface in large moving schools; open water of reservoirs and large rivers; shoreline and open water both used.
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
Spring spawningadult
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Gizzard shad spawn in shallow, protected water in spring. Threadfin begin spawning when the water warms to about 70 °F and may continue through the warmer months. Threadfin are notably cold-sensitive, with extensive die-offs reported below 45 °F — a documented thermal tolerance, not a prediction that one will happen.
Observed: Months dated from Missouri (gizzard shad). USGS gives mid-May to mid-June; South Carolina reports March through August.
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 reviewerThis entry covers gizzard and threadfin shad together. Anal-ray and scale counts on a fish in hand separate them reliably; yellow fins and a black-speckled chin on a live threadfin are field hints.MDC-GIZZARD-SHAD, USGS-NAS-GIZZARD-SHAD, MDC-THREADFIN-SHADDispute
Declared by the reviewerAdult gizzard shad outgrow what most gamefish will eat; the young-of-year fish is the forage-relevant animal.Dispute
Declared by the reviewerWinter die-offs are a documented natural event for shad in the Midwest and are not evidence of pollution.Dispute
Declared by the reviewerThis record covers gizzard and threadfin shad together. Anal-ray and scale counts on a fish in hand separate them reliably; yellow fins and a black-speckled chin on a live threadfin are field hints.MDC-GIZZARD-SHAD, USGS-NAS-GIZZARD-SHAD, MDC-THREADFIN-SHADDispute
Declared by the reviewerShad are cold-sensitive and winter die-offs are a documented natural event in the Midwest, not a sign of pollution.INDNR-SHAD-DIEOFF, USGS-NAS-GIZZARD-SHADEvidence from: Midwest winters; higher latitudesDispute
Declared by the reviewerAdult gizzard shad grow beyond the size most gamefish will take; young-of-year fish are the forage-relevant stage.MDC-GIZZARD-SHAD, SCDNR-GIZZARD-SHADDispute
Declared by the reviewerThreadfin shad are much smaller than gizzard shad, rarely over about 150 mm, and can spawn in their first summer; an adult threadfin falls inside the young-of-year size band here.MDC-GIZZARD-SHAD, MDC-THREADFIN-SHAD, ILDNR-THREADFIN-SHADEvidence from: Threadfin shad (Dorosoma petenense)Dispute
Sources disagreeThreadfin shad jaw position is described both ways. Missouri Department of Conservation's gizzard shad page and the USGS Nonindigenous Aquatic Species table say the threadfin's lower jaw projects; Missouri's own threadfin page and Illinois DNR say its upper jaw projects beyond the lower. Neither is used as a field character here.
Sources disagreeGizzard shad spawning dates differ by source and region. Missouri Department of Conservation gives early April through May; the USGS Nonindigenous Aquatic Species profile gives mid-May to mid-June; South Carolina DNR says March through August.
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 14 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.
Great Lakes Now. Live gizzard shad schooling underwater, where the keel and the trailing ray catch light differently than they do in a hand.
Science media · 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.
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