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: Eye wider than the snout is longClose look It separates Menhaden (bunker, pogy) from Alewife / river herring cleanly, and every pair of groups still in play differs on it (look closely with it still).
What to look at
Menhaden (bunker, pogy)
Alewife / river herring
Rows of small spots behind the shoulder spotdecisiveClose look
Yes
No
Eye wider than the snout is longdecisiveClose look
Not diagnostic
Yes
Body see-through, backbone or gut visibleAt a glance
No
Not diagnostic
Which way the mouth pointsClose look
Mouth angled up, lower jaw leading
Varies
Reported size
30–500 mm
4–250 mm
Water it is recorded indecisive
surf, inshore, nearshore
lake open, lake margin, river, reservoir
How it moves
dense schools that ripple or splash at the water surface; young fish corralled at the surface or tight to the shoreline in a feeding blitz
schooling in open water; moves shallow at night to spawn once the water passes about 15 degrees Celsius
Reference seasonality
Inshore season: May, Jun, Jul, Aug, Sep, Oct
Spawning run: May, Jun · Young move seaward: Jul, Aug, Sep, Oct, Nov
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 (Brevoortia)
Menhaden (bunker, pogy)
Everyone knows the shoulder spot. The shoulder spot is not the answer.
First check
Find the shoulder spot, then look BEHIND it. Rows of smaller spots trailing back is menhaden. A single spot on its own settles nothing.
What it is
A menhaden is a deep, slab-sided, oily fish with a head about a third of its body, swimming with its mouth open and straining plankton through a basket of gill rakers. In a school they ripple and splash at the surface, and when something is under them the young ones get corralled tight to the shoreline in what Massachusetts calls, in an official publication, a blitz. That is the animal most of the coast is actually fishing over.
Stages
First year (30–150 mm; the NOAA staging runs larva under 30, prejuvenile 30–38, juvenile above 38) · Full-grown (152–500 mm depending which source you read — see the limitations)
Water
surf, inshore, nearshore
Separates from Alewife / river herring
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.
Typical windows
Inshore season (adult)
Patterns (correspondence)
None mapped yet.
Limits
Adult size is stated five incompatible ways across five agencies, one of them exceeding another's stated maximum.
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 Menhaden (bunker, pogy)
This entry does not name Menhaden (bunker, pogy) as a look-alike. That is a gap in the prose, not proof they cannot be confused.
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.