Types of Fish: How Species Are Grouped

Four sorting systems, one fish

Ask what “type” a striped bass is and you can get four true answers: a saltwater fish that runs rivers, an anadromous fish, a temperate bass, and a game fish. None contradicts the others — they come from four different sorting systems, and most confusion about fish types is really confusion about which system is being used.

The scale of the problem is worth stating first. FishBase, the global species database, lists about 36,500 fish species. No angler’s list of “types” covers that; every list is a selection, organised by one of the four systems below. Our own species glossary holds 49 full profiles across all of them.

By water: fresh, salt, and the honest middle

The oldest split is where the fish lives, and the science adds a third category most lists skip. NOAA’s estuary science supplies the vocabulary: plants and animals that tolerate only slight changes in salinity are called stenohaline, and these usually live in either freshwater or saltwater environments. Those that tolerate a wide range of salinities are called euryhaline.

That third word explains every fish that refuses to stay in one list. Striped bass in a reservoir and in the surf, snook in a river mouth, black drum far up an estuary — euryhaline species work both sides of the salt line, and our profiles mark them “Fresh & Saltwater” for exactly this reason.

By migration: fish with two addresses

Some fish are typed by their commute. NOAA describes Atlantic salmon as anadromous — they live in both fresh and salt water, hatching in freshwater rivers, migrating to the ocean where they mature, and returning to their natal rivers to spawn. Every Pacific salmon in our glossary, from chinook to pink, runs this schedule, as do some striped bass and coastal cutthroat trout.

Catadromous fish run it in reverse. The Susquehanna River Basin Commission describes the American eel plainly: a catadromous species that spawns in the Atlantic Ocean and travels upstream into fresh water to live the majority of its 10-to-30-year life. Born at sea, resident in rivers — the salmon’s mirror image.

By family: the groupings biology actually supports

Families are where “types” stop being labels and start carrying real shared traits. Minnesota’s game-fish statute usefully names the freshwater core, family by family: Centrarchidae — the sunfishes and black bass, from bluegill to largemouth; Percidae — walleye, sauger and yellow perch; Salmonidae — the trout and salmon; Ictaluridae — the catfishes; and Esocidae — northern pike and muskellunge.

Salt water adds its own cores, each with a defining habit. Scombridae, the mackerels and tunas, are the open-water speed family — NOAA’s mackerel profile notes they school near the surface and travel between spawning and summering grounds. Sciaenidae are the drums, named for what they do: Texas Parks and Wildlife notes that red drum and their relatives make drumming sounds by vibrating a muscle against the swim bladder — our black drum profile covers the loudest of them. Serranidae, the true sea basses and groupers, carry the strangest trait: NOAA describes black sea bass as protogynous hermaphrodites, most starting as females and becoming males as they grow. Carangidae are the jacks, from permit to greater amberjack; Labridae the wrasses, whose local representative is the tautog.

One split sits above all the families: nearly everything an angler catches is a bony fish. Sharks and rays are elasmobranchs — NOAA translates the term as fish made of cartilaginous tissue, the clear gristly stuff of ears and nose tips — a separate branch entirely.

By law: the type that changes at the state line

The fourth system is the one anglers argue about most, and it is not biology at all. “Game fish” and “rough fish” are legal categories, written by state legislatures, and Minnesota’s statute proves the point inside a single family: blue, channel and flathead catfish are statutory game fish, while black, brown and yellow bullheads — members of the same catfish family — are statutory “native rough fish”.

Nothing about a bullhead’s biology demoted it; a law did, and a different state’s law draws the line elsewhere. The same shift is happening to common carp, managed as a nuisance in one state and promoted as a hard-fighting sport fish in the next. So treat legal type the way this site treats every regulation: your state’s fish and wildlife code defines the list that applies to you, and it is the only version worth acting on.

Using the types

The practical payoff of keeping the four systems straight is knowing which question you are asking. Where can I fish for it — a water question. When will it be in the river — a migration question. What will its relatives behave like — a family question. May I keep it — a legal question, answered only by your state.

Our species glossary is organised to serve all four: every profile states water type, family, and migration where it applies — and points regulation questions at the agencies, where they belong.