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: Body see-through, backbone or gut visibleAt a glance It separates Mullet (young) from Silversides cleanly, and every pair of groups still in play differs on it and you can check it at a glance.
What to look at
Mullet (young)
Silversides
Blunt flat head with a small mouthdecisiveClose look
Yes
No
Which way the mouth pointsdecisiveClose look
None of these
Mouth angled up, lower jaw leading
Body see-through, backbone or gut visibledecisiveAt a glance
No
Yes
Head wide and flattened, wider than the bodydecisiveAt a glance
Not diagnostic
No
Eye wider than the snout is longdecisiveClose look
Not diagnostic
Yes
Deep, slab-sided bodyAt a glance
Not diagnostic
No
Reported size
15–698 mm
25–445 mm
How it moves
leaps clear of the water, sometimes a metre up; one of its common names is jumping mullet; schools by day for protection
schooling, close to the surface; moves offshore in winter — one assessment records up to about ninety miles
Reference seasonality
Autumn migration: Sep, Oct, Nov
Estuary spawn: Apr, May, Jun, Jul
The same for both: water, 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
Mugil cephalus, Mugil curema
Mullet (young)
Blunt head, small mouth, two back fins, and a habit of leaving the water for no reason anyone can prove.
First check
Look at the head end. Blunt, flat, and a small mouth at the very front, with two widely separated back fins behind it — mullet.
What it is
Mullet are the one fish in this wave that everybody has watched and almost nobody has looked at. They jump — sometimes a metre clear — and four different agencies give four different explanations for why. To evade predators. To clean the gills. To get oxygen out of warm stagnant water. And, from Connecticut, with admirable directness: for unclear reasons. Four sourced answers and no settled one is a perfectly good thing for a field guide to say.
Stages
First year (15–178 mm; pre-juveniles reach the outer beaches at 20–25 mm and enter North Carolina estuaries at about 22 mm) · Full-grown (283–698 mm for North Carolina striped mullet (males mature at 283 mm, females at 319); white mullet are common only to about 330 mm; larger maxima published elsewhere)
Water
surf, inshore, nearshore
Separates from Silversides
Both carry two dorsals. Connecticut states the separation directly: a young mullet has fewer anal rays and the anal fin starts directly under the dorsal.
Typical windows
Autumn migration (adult)
Patterns (correspondence)
None mapped yet.
Limits
The phrase “mullet run” is used by no source consulted; North Carolina records fishermen calling the movement a “mullet blow”. “Finger mullet” is North Carolina's name for young-of-year mullet.
The band down the side is the easy part. Count the back fins.
First check
Count the dorsal fins. Two, with a clear gap, on a slim fish with a bright band down the side — silverside. One dorsal — go and look at the anchovy and menhaden entries instead.
What it is
A silverside is the fish most people picture when they say bait: slim, translucent-green over the back, and carrying a bright metallic band the whole length of the flank. The band is what you notice from the bank, and it is also what gets people into trouble, because a bay anchovy has a stripe too. The difference is that a silverside's is thick and iridescent and runs all the way forward, and an anchovy's is narrow and often fades out toward the head — and fades after death.
Stages
First year (No Atlantic first-year length in the sources; Pacific topsmelt reach 64–102 mm and jacksmelt average 114 mm in their first year) · Full-grown (51–178 mm for the Atlantic silverside, commonly 76–102 mm; Pacific jacksmelt reach 445 mm and topsmelt 368 mm)
Water
surf, inshore, nearshore
Separates from Mullet (young)
Mullet also carry two separated dorsals — this is the honest confusion. The head settles it: a mullet's is blunt and flattened with a small mouth at the front, a silverside's is short with the jaw angled up. Connecticut adds the count: a young mullet has fewer anal rays, and its anal fin starts directly under the dorsal.
Typical windows
Estuary spawn (adult)
Patterns (correspondence)
Epoxy Silverside
Limits
This is the family, not a species. Atlantic and inland silverside are described as very difficult to separate without magnification.