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Black Bass · Centrarchidae

Largemouth Bass

Micropterus nigricans

The most widely stocked freshwater gamefish in the world, renamed Micropterus nigricans in 2023 when genetic work showed the name salmoides belonged to the Florida bass.

Largemouth Bass (Micropterus nigricans)
Largemouth Bass. Raver, Duane, Public domain. Source.

Identification

The largemouth bass is a deep-bodied, laterally compressed sunfish with a ragged dark band running the length of the midside. The band is bold in clear water and nearly invisible in stained water, and in older fish it commonly breaks into a chain of blotches rather than a continuous stripe.

Two features separate it reliably from the other black basses of North America. The first is the jaw: in adults the rear edge of the maxilla extends clearly past the back of the eye, which no other Micropterus does consistently. The second is the dorsal fin, which is nearly divided in two — a deep notch drops almost to the back between the spiny front section, which carries nine spines, and the soft-rayed rear section of twelve to thirteen rays (Texas Parks and Wildlife Department). Spotted bass, by contrast, have the two fins broadly connected and a rough patch of small teeth on the tongue that largemouth lack.

Scale counts distinguish largemouth bass from the closely related Florida bass, which is otherwise visually identical: the Florida bass carries 69–73 scales along the lateral line against 59–65 in the largemouth (Florida Museum of Natural History). Because the ranges overlap across a wide intergrade belt, and because the two interbreed freely wherever stocking has mixed them, field identification of the two is unreliable and Florida’s own wildlife agency advises anglers not to attempt it.

A recent change of scientific name

For roughly seventy-five years the largemouth bass was called Micropterus salmoides. It is not, and never was.

In 2022 Daemin Kim, Andrew Taylor and Thomas Near published a genome-scale phylogeny of the black basses in Scientific Reports, using ddRAD sequence data to delimit nineteen species of Micropterus — fourteen already described, three known but undescribed (Altamaha, Bartram’s and Choctaw basses) and two unnamed smallmouth lineages. In the course of that work they re-examined the type material behind Lacépède’s 1802 description of salmoides and concluded that it refers to the Florida bass, not to the widespread continental fish. The correct available name for the largemouth bass, Micropterus nigricans (Cuvier), was accordingly elevated from synonymy, and Micropterus floridanus became a junior synonym of salmoides (Kim, Taylor and Near 2022; PubMed record).

The American Fisheries Society adopted the change in the eighth edition of Common and Scientific Names of Fishes from the United States, Canada, and Mexico (Page et al. 2023, AFS Special Publication 37), which is the standard naming authority for North American fishes and is issued jointly with the American Society of Ichthyologists and Herpetologists. The practical result is a swap: largemouth bass is now Micropterus nigricans, and Micropterus salmoides now means Florida bass (AFS Ontario Chapter summary of the 2023 changes).

Agencies have moved at different speeds. Florida’s Fish and Wildlife Conservation Commission recognised the Florida bass as a distinct species and incorporated the new names at its February 2025 meeting (FWC, FWC news release). Maryland’s Department of Natural Resources went through a formal process to update the binomial in its own documents so that they “refer to the proper species of black bass” (Maryland DNR). NatureServe now carries separate records for M. nigricans and for M. salmoides as Florida bass. But a great many public agency pages still print the old name: as of writing, the species accounts published by Texas Parks and Wildlife, the Wisconsin DNR and the Florida Museum of Natural History all still use Micropterus salmoides for the largemouth bass. Readers should expect to meet both names for years yet.

One consequence matters for everything below: essentially the entire body of published work on largemouth bass biology — thermal tolerance, growth, spawning, diet — was produced under the name M. salmoides. In most cases those studies were working on fish now called M. nigricans, or on intergrades. The findings did not change; only the label did.

Range and distribution

The native range covers the St. Lawrence–Great Lakes and Hudson Bay (Red River) drainages, the Mississippi basin from southern Quebec and Ontario to Minnesota and south to the Gulf, and Gulf Slope drainages reaching the Rio Grande system of southern Texas and northern Mexico (NatureServe; USGS Nonindigenous Aquatic Species database). The Atlantic Coastal Plain from peninsular Florida north to North Carolina is Florida bass country, with three genetically distinct clusters recognised across Florida rivers, the Atlantic Piedmont and the Atlantic Coastal Plain (NatureServe, Florida bass).

Beyond that, the map is an artefact of a century of hatchery work. Largemouth bass have been moved into essentially every warmwater drainage on the continent and into more than fifty countries. Much of that introduced stock is of Florida-bass or intergrade origin, which is why the new taxonomy is awkward to apply outside the native range.

Habitat and water temperature

In rivers, largemouth bass are a low-velocity animal. Missouri’s fish and wildlife agency places them in “lowland lakes, artificial impoundments of all sizes, permanent pools of streams, and quiet backwaters of large rivers” — a description that separates them cleanly from smallmouth in cool clear Ozark current and from spotted bass in permanently flowing, warmer, more turbid water (Missouri Department of Conservation).

Telemetry work quantifies how strong that preference is. A three-year study of radio-tagged largemouth in the Kissimmee River, Florida, found current velocities of less than 6 cm per second at a minimum of 92.2% of bass locations in any season, with fish concentrated in smartweed, spatterdock and aquatic grass. Daily movements averaged under 100 m for more than half of all location samples. Fish held home areas where dissolved oxygen stayed above 2 ppm year-round, and abandoned them — moving more than a kilometre — when acute oxygen declines dropped water below that between June and October (Furse, Davis and Bull 1996). In a river, largemouth bass are eddy and slackwater fish, and oxygen, not current, is what usually forces them to move.

Thermally the species is warm-adapted and unusually tolerant. Nevada’s Division of Environmental Protection compiled the published literature and reports:

  • Optimal growth: 25–30°C (77–86°F) for fastest growth (Coutant and DeAngelis 1983); 28.1–28.6°C (82.6–83.5°F) in Díaz et al. 2007; 27.5–30°C (81.5–86°F) in Strawn 1961.
  • Preferred temperature: 27–32°C (80.6–89.6°F) for adults (Venables et al. 1978); a final preferendum of 29.0°C (84.2°F) (Neill and Magnuson 1974).
  • Upper incipient lethal temperature: 32.7–36.4°C (90.9–97.5°F) at high acclimation (Hart 1952), but as low as 30.6–31°C (87.1–87.8°F) at 22°C acclimation (McCormick and Wegner 1981).
  • Critical thermal maximum: 36.7°C (98°F) at 20°C acclimation up to 38.2–39.8°C (100.8–103.6°F) at 30–36°C acclimation.

Nevada DEP recommends a chronic threshold of 32°C (89.6°F) and an acute threshold of 34°C (93.2°F) for juveniles and adults (Nevada DEP thermal tolerance analysis). The acclimation dependence in that list is not a footnote — it is the main point. A largemouth that has spent August in 88°F water can survive temperatures that would kill a fish moved there from 72°F.

Early life stages are the constraint. Storms, Foltz and Wilde tested pro-larvae and post-larvae and calculated a maximum weekly average temperature of 28.1°C (82.6°F) to protect them, with 96-hour TL50 values of 32.8°C for instant exposure and 34.1°C when temperature rose gradually at 5°C per day (Storms et al. 1986). A gauge reading of 84°F in July therefore means two different things at once: comfortable for adults, above the protective ceiling for that year’s fry.

Life history

Spawning is a male enterprise. The male fans a saucer-shaped nest, usually on sand or gravel but readily on soft bottom where roots, twigs and snail shells give the eggs something to adhere to, then guards eggs and fry.

Reported temperature triggers vary, and the variation is worth stating plainly. Wisconsin reports spawning from late April to early July, beginning when water reaches 60°F, with eggs laid at 62–65°F (Wisconsin DNR). Texas gives a start near 60°F, occurring anywhere from February to May depending on latitude (TPWD). The Florida Museum states the species “generally does not spawn at temperatures much below 64°F (17.8°C),” with optimum conditions around 18.9–20.0°C. Part of that spread is latitude and part is definition — the onset of nest-building runs several degrees ahead of egg deposition — but the sources do disagree, and 60°F is best read as the point at which nesting behaviour begins rather than the point at which eggs are in the gravel.

Fecundity estimates also conflict: TPWD gives 2,000–43,000 eggs per nest, while the Florida Museum reports 2,000–145,000, a range that probably reflects the inclusion of very large Florida-strain females. Eggs hatch in five to ten days. Growth in Texas runs to 4–6 inches in the first year, 8–12 inches by age two and about 16 inches by age three. Longevity is contested: TPWD cites an average lifespan up to 16 years, whereas the Florida Museum gives maximum ages of about nine years for females and six for males. The higher figure is likely a maximum rather than an average.

Diet

Largemouth bass are gape-limited generalists and the diet tracks mouth size. Fry take zooplankton, then insect larvae; by about two inches they are eating fish and large invertebrates such as crayfish, and cannibalism is routine (TPWD). Adult stomach contents run to small fish, crayfish, mussels, snails, adult and larval insects, tadpoles and frogs (Florida Museum). In river backwaters this typically means sunfish, shad, minnows and crayfish, in proportions set by whatever the slackwater holds.

Behaviour and angling

Nearly everything characteristic about how largemouth bass behave follows from being a short-burst ambush predator with a very large mouth and a low tolerance for sustained swimming. The species does not hold in current and does not chase over distance. It waits beside an edge — a weed line, a laydown, an undercut bank, the seam where an eddy meets moving water — and takes prey in one or two body lengths. In a river this pushes the fish out of the thalweg and into backwaters, sloughs, oxbows, tributary mouths and the dead water behind wood, which is exactly the distribution the Kissimmee telemetry recorded.

Metabolic rate scales with temperature, and so does feeding frequency. Wisconsin’s summary that “few bite in the winter” is a plain-language statement of a real physiological floor: below roughly 50°F a largemouth’s daily ration collapses and feeding becomes episodic rather than daily. At the other end, fish sitting in water in the high 80s are feeding hard but are also close to their chronic thermal ceiling, and in shallow river backwaters that heat is coupled to oxygen depletion — which is why summer largemouth in rivers so often relocate abruptly rather than merely going deeper.

Spring behaviour is nest-driven and shallow; the fish are visible, territorial and site-attached. Post-spawn they disperse to cover. Because river largemouth move so little, individual backwaters function as semi-independent populations, and a slough that fishes well one year will often fish well the next for the same reason a pool holds the same smallmouth: the fish never left.

Conservation

Largemouth bass are in no danger. NatureServe has not yet assigned a global rank to Micropterus nigricans following the split, listing it as GNR, and the same applies to the Florida bass — this reflects the newness of the taxonomy rather than any concern about abundance (NatureServe). There is no federal listing.

The conservation problems attached to this species run the other way. Outside its native range it is an effective introduced predator: USGS attributes declines of native ranid frogs in California and of California tiger salamander populations partly to introduced predatory centrarchids including largemouth bass (USGS NAS). There is also a genetic dimension that the 2023 renaming has made newly visible. Decades of stocking Florida-strain fish into largemouth waters, chasing larger average size, has produced intergrade populations across much of the southern United States. Those fish are now, formally, hybrids between two recognised species, and the practice has blurred a boundary that biologists are only now able to describe properly.

Where to catch it

609 waterways on GuidedFloats list largemouth bass, across 48 states. Each page carries live gauge readings, access notes, and the guides who fish it.

Alabama 18

Arizona 9

Arkansas 18

California 15

Colorado 3

Connecticut 4

Delaware 9

Florida 20

Georgia 15

Hawaii 9

Idaho 5

Illinois 17

Indiana 20

Iowa 9

Kansas 18

Kentucky 16

Louisiana 73

Maine 2

Maryland 6

Massachusetts 12

Michigan 9

Minnesota 6

Mississippi 16

Missouri 15

Montana 1

Nebraska 14

Nevada 9

New Hampshire 7

New Jersey 4

New Mexico 9

New York 9

North Carolina 14

North Dakota 6

Ohio 20

Oklahoma 20

Oregon 4

Pennsylvania 5

Rhode Island 12

South Carolina 21

South Dakota 4

Tennessee 16

Texas 51

Utah 2

Vermont 6

Virginia 12

Washington 3

West Virginia 4

Wisconsin 12

References

  1. Phylogenomics and species delimitation of the economically important Black Basses (Micropterus) — Scientific Reports (Kim, Taylor and Near 2022)
  2. Phylogenomics and species delimitation of the economically important Black Basses (Micropterus) — PubMed record — National Library of Medicine
  3. Common and Scientific Names of Fishes from the United States, Canada, and Mexico, 8th edition (Special Publication 37) — American Fisheries Society
  4. Changes to Fish Names – 2023 — Ontario Chapter, American Fisheries Society
  5. Largemouth Bass — Scientific Renaming — Maryland Department of Natural Resources
  6. New name, same fish: Largemouth bass are now Florida bass — Florida Fish and Wildlife Conservation Commission
  7. FWC: Florida bass is a unique species — Florida Fish and Wildlife Conservation Commission
  8. Florida Bass / Largemouth Bass species profile — Florida Fish and Wildlife Conservation Commission
  9. Micropterus nigricans — Largemouth Bass — NatureServe Explorer
  10. Micropterus salmoides — Florida Bass — NatureServe Explorer
  11. Largemouth Bass — Species Profile, Nonindigenous Aquatic Species database — U.S. Geological Survey
  12. Largemouth Bass Thermal Tolerance Analysis — Juvenile and Adult, Summer — Nevada Division of Environmental Protection
  13. Upper Thermal Tolerance of Early Life Stages of South Carolina and Florida Largemouth Bass (Storms, Foltz and Wilde 1986) — Proceedings of the Annual Conference SEAFWA 40:57–64
  14. Habitat Use and Movements of Largemouth Bass Associated with Changes in Dissolved Oxygen and Hydrology in Kissimmee River, Florida (Furse, Davis and Bull 1996) — Proceedings of the Annual Conference SEAFWA 50:12–25
  15. Largemouth Bass species account — Texas Parks and Wildlife Department
  16. Largemouth bass — Fishes of Wisconsin — Wisconsin Department of Natural Resources
  17. Black Bass — Missouri Department of Conservation
  18. Largemouth Bass — Discover Fishes species profile — Florida Museum of Natural History, University of Florida
  19. IGFA World Records — International Game Fish Association