The largemouth bass, Micropterus salmoides, is one of the best-known game fishes in North America. Micropterus refers to a small dorsal fin. While salmoides means trout-like (Heidinger 1976). The bodies are slightly compressed laterally but slender to robust overall and oval in the cross-section (Becker 1983). Terminally positioned mouths are large and extend past the eye with villiform teeth inside (Heidinger 1976; Keast & Webb 1966). Eyes are golden brown in color (Becker 1983). Spinous and soft-rayed sections of the dorsal fin combine into one at a small intersection. Dorsal fin has 8-11 dorsal spines and 11-14 dorsal rays. Anal fin has 2-3 anal spines and 10-12 anal rays. Lower lobe of the operculum is considerably longer than the upper lobe. 31-33 vertebrate with 14-15 being precaudal (Heidinger 1976). 60-68 ctenoid scales along the lateral line (Becker 1983). 9-20 rows of scales on the cheek (Heidinger 1976). Coloration is usually green dorsally and white ventrally while immature bass have a black stripe on the side of their bodies that fades as they reach maturity (Phillips et al. 1982). Back section of the caudal fin is darker than the base of the caudal fin. Around the urogenital opening, males have a circular-shaped, scaleless area while that area is elliptical or pear-shaped in females (Heidinger 1976).

When mature, males are 22 cm and females are 25 cm on average in total length (Heidinger 1976). On average, largemouth bass have a lifespan of 6 or 7 years but can reach a maximum age of 15 years (Heidinger 1976; Stewart & Watkinson 2004). The world record largemouth bass is 10.12 kg and 65.0 cm in total length (IGFA 2019). In contrast, the Minnesota state record is considerably smaller at 4.05 kg and 59.69 cm in total length (MN DNR 2019).

Systematics:  

he Centrarchidae family includes black basses, rock basses, crappies, and sunfishes. This family includes a total of 32 species. The centrarchids are typically the dominant top-level predator fishes in North American freshwater lakes and rivers. Family fossils found in Montana show a long history and date back all the way to the Eocene era (Near et al. 2004).

Four major centrarchid lineages exist including Acantharchus pomotis, Micropterus, Lepomis, and a clade that contains Ambloplites, Archoplites, Centrarchus, Enneacanthus, and Pomoxis (Near et al. 2004). Micropterus, the black bass genus, and Lepomis, the sunfish genus, are sister genera within the Centrarchidae family. The sister species of the largemouth bass, Micropterus salmoides, is Micropterus treculi, the Guadalupe bass (Johnson et al. 2001; Near et al. 2004).

Phylogenetic research has strongly supported that largemouth bass are separated into two distinct species (Maceina et al. 1988; Near et al. 2004). Those species are the northern largemouth bass (Micropterus salmoides salmoides) and the Florida largemouth bass (Micropterus salmoides floridanus). The Florida largemouth bass is native to Florida while the northern largemouth bass can be found everywhere else in North America. These species can hybridize though so hybrids can be seen anywhere in the largemouth bass native range (Maceina et al. 1988).

Largemouth bass are native to the U.S., Canada, and Mexico but they have been introduced and still exist all over the world. The true native range generally runs north to south along the Mississippi River (Heidinger 1976). They are mostly found in the central or eastern portion of the U.S. (Johnson et al. 2001).

Habitat preference for largemouth bass can generally be described as shorelines of lakes and rivers at shallow depths. They inhabit small- and medium-size lakes that have clear water and sandy shorelines. Backwaters along rivers like the Mississippi and St. Croix are also ideal locations for largemouth bass to live (Phillips et al. 1993). In lakes with large amounts of vegetation and coarse woody debris (like logs and branches) these fish like to stay within 100 meters of their habitat (Ahrenstorff et al. 2009; Winter 1977). That habitat is usually somewhere along a shoreline at less than 3 meters deep with typical substrates of sand, gravel, or mud (Ahrenstorff et al. 2009; Becker 1983). Within these habitat requirements, they have even more specific areas they use for reproduction. Largemouth bass will look for some type of structure to reproduce. Those structures are ideally logs or stumps but can also include small branches, tree roots, and boulders. They will not reproduce in habitat lacking structures (Hunt & Annett 2002).

Other Interesting Facts:  

The length of largemouth bass differs within populations based on latitudes. Populations in higher latitudes will have smaller mean lengths than populations in lower latitudes (Helser & Lai 2004).

Largemouth bass and smallmouth bass (Micropterus dolomieui) can hybridize to create what is called a meanmouth bass. Meanmouth bass are fertile but have only been hybridized artificially because they are extremely aggressive. These have not been used when stocking fisheries because they may eliminate the largemouth and smallmouth populations based on their aggressive nature (Becker 1983).

Food:  

Largemouth bass feed on crayfish, young black bullheads, bullfrog tadpoles, green sunfish, zooplankton, mollusks, and insects (Heidinger 1976; Near et al. 2004). When feeding, they swallow organisms whole and seem to be more effective in catching organisms that are long and cylindrical rather than compressed (Heidinger 1976).

This species uses a strike response feeding maneuver based on reflexes. This usually happens when the bass is swimming and sees prey at a distance. The outcome is they either suck in and swallow the baitfish at a high velocity or miss them completely (Heidinger 1976).

In terms of feeding times throughout the day, largemouth bass are not particular and are known to eat at any time of the day. There are two specific periods they do not feed though. One is during the spawning period while they are guarding the nest. While the second is when temperatures are above 37° C or below 5° C (Heidinger 1976).

Reproduction:  

When mature, largemouth bass will begin to build nests to reproduce. Age at maturity is variable at 8 months to 1 year in tropical areas or 3-5 years in northern parts of their range. Once maturity is reached, males build nests in the spring when temperatures are around 15-24° C. Their nests are usually 0.33-1.33 m deep and generally near rocks or stumps to provide protection from wind events. The male will create a nest by moving his head in debris to push it around, then pivots in a circle to create a nest which usually ends up being the length of the male creating the nest (Heidinger 1976). Nest substrates usually consist of sand, gravel, or mud (Becker 1983).

Males attract ripe females to their nests using an aggressive courting strategy which involves continuous color pattern changes. Males nip, butt, or push females to stimulate them at the nest. The male and female are next to each other over the nest when spawning begins, and each violent jerk of their bodies usually means that eggs are fertilized and go into the nest below. This usually lasts for 30 minutes. Nests will have between 5,000-43,000 eggs. Eggs are usually yellow or orange, semi-opaque, and 1.4 to 1.8 mm in diameter (Heidinger 1976).

The female leaves the nest after spawning and may continue to lay eggs in more than one nest. The male stays to guard the nest and does not eat for weeks until the fry hatch. The male will allow golden shiners (Notemigonus crysoleucas) and lake chubsuckers (Erimyzon sucetta) to lay eggs in the same nest they are guarding but all other fish species are considered predators and will be warded off (Heidinger 1976).

Largemouth bass are important for sport fishing. Anglers who fish for largemouth bass are generally looking for trophy fish rather than to keep the bass to eat (Spencer 1993). This has led to the creation of many bass fishing tournaments around North America (Heidinger 1976). Largemouth bass fishing has produced significant gains for some local economies. One study done by Chen et al. (2003) on a largemouth bass trophy fishery in Lake Fork, Texas even showed that bass fishing added $9,355,999 and 367 jobs to the local economy.

According to Jelks et al. (2008), the largemouth bass is a threatened species and its status has declined since 1989 mostly because its habitat is restricted and being reduced. Minimum length catch limits have been used in different areas but no evidence has been shown that these limits help the bass populations. During fishing tournaments, catch and release methods are implemented after weighing the fish to limit the possibility of overfishing these areas (Heidinger 1976).

Habitat improvements including lake destratification, acid water neutralization, and cow fencing around farm ponds have been completed in the past but are difficult to accomplish at large scales. On a small scale, fertilizing new ponds using 8-8-2 fertilizer has shown to double the amount of largemouth bass (Heidinger 1976).

Largemouth bass do not have many known disease issues but largemouth bass virus (LMBV) is one currently being monitored. It generally affects relatively large bass that are 20-38 cm in total length. LMBV causes the swim bladder to be over-inflated and can lead to fish kill. LMBV infected bass are likely to be relatively low in weight. Fortunately, some bass seem to survive with the infection (Grizzle & Brunner 2003).

Ahrenstorff, T.D., Sass, G.G., Helmus, M.R. 2009. The influence of littoral zone coarse woody habitat on home range size, spatial distribution, and feeding ecology of largemouth bass (Micropterus salmoides). Hydrobiologia 623(1): 223-233.

Becker, G.C. 1983. Fishes of Wisconsin. University of Wisconsin Press, Madison.

Chen, R.J., Hunt, K.M., Ditton, R.B. 2003. Estimating the economic impacts of a trophy largemouth bass fishery: issues and applications. North American Journal of Fisheries Management 23(3): 835-844.

Grizzle, J.M., Brunner, C.J. 2003. Review of largemouth bass virus. Fisheries 28(11): 10-14.

Heidinger, R.C. 1976. Synopsis of biological data on the largemouth bass, Micropterus salmoides (Lacepéde) 1802. Food and Agriculture Organization of the United Nations, Rome.

Helser, T.E., Lai, H.L. 2004. A Bayesian hierarchical meta-analysis of fish growth: with an example for North American largemouth bass, Micropterus salmoides. Ecological Modelling 178(3-4): 399-416.

Hunt, J., Annett, C.A. 2002. Effects of habitat manipulation on reproductive success of individual largemouth bass in an Ozark reservoir. North American Journal of Fisheries Management 22(4): 1201-1208.

IGFA World Records Search. Retrieved September 2019. https://igfa.org/igfa-world-records-search/?search_type=CommonNameSummary&search_term_1=Bass,+largemouth.

Jelks, H.L., Walsh, S.J., Burkhead, N.M., Contreras-Balderas, S., Diaz-Pardo, E., Hendrickson, D.A., Lyons, J., Mandrak, N.E., McCormick, F., Nelson, J.S., Platania, S.P., Porter, B.A., Renaud, C.B., Schmitter-Soto, J.J., Taylor, E.B., Warren, M.L. 2008. Conservation status of imperiled North American freshwater and diadromous fishes. Fisheries 33(8): 372-407.

Johnson, R.L., Magee, J.B., Hodge, T.A. 2001. Phylogenetics of freshwater black basses (Centrarchidae: Micropterus) inferred from restriction endonuclease analysis of mitochondrial DNA. Biochemical genetics 39(11-12): 395-406.

Keast, A., Webb, D. 1966. Mouth and body form relative to feeding ecology in the fish fauna of a small lake, Lake Opinicon, Ontario. Journal of the Fisheries Board of Canada 23(12): 1845-1874.

Maceina, M.J., Murphy, B.R., Isely, J.J. 1988. Factors regulating Florida largemouth bass stocking success and hybridization with northern largemouth bass in Aquilla Lake, Texas. Transactions of the American Fisheries Society 117(3): 221-231.

Near, T.J., Bolnick, D.I., Wainwright, P.C. 2004. Investigating phylogenetic relationships of sunfishes and black basses (Actinopterygii: Centrarchidae) using DNA sequences from mitochondrial and nuclear genes. Molecular Phylogenetics and Evolution 32(1): 344-357.

Phillips, G.L., Schmid, W.D., Underhill, J.C. 1982. Fishes of the Minnesota Region. University of Minnesota Press, Minneapolis.

Spencer, P.D. 1993. Factors influencing satisfaction of anglers on Lake Miltona, Minnesota. North American Journal of Fisheries Management 13(2): 201-209.

State record fish programs - Minnesota DNR. Retrieved September 2019. https://www.dnr.state.mn.us/fishing/staterecords.html.

Stewart, K.W., Watkinson, D.A. 2004. The Freshwater Fishes of Manitoba. University of Manitoba Press, Winnipeg.

Winter, J.D. 1977. Summer home range movements and habitat use by four largemouth bass in Mary Lake, Minnesota. Transactions of the American Fisheries Society 106(4): 323-330.