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 Sunfish, young of year 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
Sunfish, young of year
Shiners and minnows
Spiny front dorsal fin (perch, sunfish)decisiveIn hand
Yes
No
One soft dorsal fin, no spinesdecisiveClose look
No
Yes
Dark ear flap on the gill coverdecisiveClose look
Yes
No
Dark vertical bars down the flankdecisiveAt a glance
Yes
Not diagnostic
Deep, slab-sided bodydecisiveAt a glance
Yes
Not diagnostic
Rounded, cigar-shaped bodydecisiveAt a glance
No
Not diagnostic
Blunt flat head with a small mouthClose look
No
Not diagnostic
Dorsal fin layoutClose look
Varies
None of these
Reported size
21–50 mm
38–230 mm
Water it is recorded in
lake margin, reservoir, river, stream
lake margin, lake open, river, stream, reservoir
Life stages covered
young-of-year
young-of-year, adult
How it moves
holding in and around weed and cover by day; juveniles may move into open water at night
schooling; emerald shiners spawn at night in shallow water over sand or mud
Reference seasonality
Colonial nesting: May, Jun, Jul, Aug
No family-level window
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
Centrarchidae (Lepomis)
Sunfish, young of year
Deep as a coin, with a dark ear flap.
First check
One joined or barely divided dorsal fin on a very deep body, and no spines on the gill cover. That is a sunfish, not a perch.
What it is
A young sunfish is spiny-rayed like a perch, so the first cut puts them in the same half of the key. What separates them is the shape and the flap.
Stages
Young of year (21–50 mm in the first year)
Water
lake-margin, reservoir, river, stream
Separates from Shiners and minnows
No spines at all means a minnow. Sunfish carry three or more anal spines alone.
Typical windows
Colonial nesting (young-of-year)
Patterns (correspondence)
None mapped yet.
Limits
In Iowa, first-year bluegill average roughly 25–50 mm; in one Indiana lake, fry returned from open water to cover at 21–25 mm.
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 Sunfish, young of year
This entry does not name Sunfish, young of year 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.