The comparison scores every group at once. This page is for the moment you already have a pair of names in mind — mayfly or stonefly, scud or sowbug, shad or alewife — and want the structures that keep them apart, in one look. Nothing here is a current hatch.
The differences, and nothing else
Best separating check: Deep, slab-sided bodyAt a glance It separates Alewife / river herring from Shiners and minnows cleanly, and every pair of groups still in play differs on it and you can check it at a glance.
What to look at
Alewife / river herring
Shiners and minnows
Sawtooth belly keel you can feeldecisiveIn hand
Yes
No
Dark spot behind the gill coverdecisiveAt a glance
Yes
Not diagnostic
Deep, slab-sided bodydecisiveAt a glance
Yes
Not diagnostic
Eye wider than the snout is longdecisiveClose look
Yes
Not diagnostic
Blunt flat head with a small mouthClose look
No
Not diagnostic
Rounded, cigar-shaped bodyAt a glance
No
Not diagnostic
Dark vertical bars down the flankAt a glance
No
Not diagnostic
Reported size
4–250 mm
38–230 mm
Water it is recorded in
lake open, lake margin, river, reservoir
lake margin, lake open, river, stream, reservoir
How it moves
schooling in open water; moves shallow at night to spawn once the water passes about 15 degrees Celsius
schooling; emerald shiners spawn at night in shallow water over sand or mud
Reference seasonality
Spawning run: May, Jun · Young move seaward: Jul, Aug, Sep, Oct, Nov
No family-level window
The same for both: life stages.
Rows come from the reviewed diagnostic weights the comparison scores with. “Decisive” means one answer puts them at least four points apart — the carrier's own rule for a structure that separates a pair.
The two entries, side by side
Clupeidae (Alosa pseudoharengus)
Alewife / river herring
The sawbelly with the oversized eye.
First check
Is the eye wider than the snout is long, with no thread on the back fin? That is alewife rather than shad.
What it is
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.
Stages
Young of year (About 4 mm at hatching; in the Great Lakes, about 60–100 mm by autumn)
Water
lake-open, lake-margin, river, reservoir
Separates from Shiners and minnows
A sawtooth belly rules out every minnow. The golden shiner's belly keel is soft and scaleless, not saw-edged.
Typical windows
Spawning run (adult) · Young move seaward (young-of-year)
Patterns (correspondence)
None mapped yet.
Limits
Landlocked Great Lakes alewife are much smaller than the anadromous Atlantic form; the sizes here follow Great Lakes survey figures.
no reviewed plateNo plate is drawn for this group, and that is a decision rather than a backlog item. This family is identified by what is missing — no belly keel, no spines, no adipose fin, no thread off the back fin — so a drawing of one shiner would be asserting a shape the record does not claim for the family. Read the four absences below instead. A plate becomes possible here the day this entry narrows to a named species.
Cyprinidae
Shiners and minnows
One soft fin, no saw on the belly, nothing else to it.
First check
Run a finger along the belly, look at the front of the back fin, and check behind it. No saw-edged belly, no spines and no adipose fin is a minnow.
What it is
In forage terms the plainest family: a small fish with one soft dorsal fin, no spines anywhere, no saw-edged belly and no adipose fin. Almost every identification here is made by what is absent.
Stages
Adult (38–230 mm across four common baitfish species)
Water
lake-margin, lake-open, river, stream, reservoir
Separates from Alewife / river herring
This entry does not name Alewife / river herring as a look-alike. That is a gap in the prose, not proof they cannot be confused.
Typical windows
No family-level window in this layer.
Patterns (correspondence)
None mapped yet.
Limits
Family-level only. Species separation within Cyprinidae is not supported here.