FISH OF MISSISSIPPI
Warmouth (Lepomis gulosus)
BRYANT HALEY
Department of Wildlife and Fisheries, Mississippi State University, Mississippi State, MS 39762
USA
Abstract—Lepomis gulosus (Curvier 1829) is a sunfish commonly called the warmouth. It is a
freshwater fish found throughout the eastern and southeastern portion of the United States. The
warmouth are able to tolerate a variety of habitat conditions allowing them to survive in waters
with low levels of oxygen and to thrive in areas of elevated salinity and temperature. They are
omnivores and eat a variety of foods. No conservation concerns exist for the warmouth in the
south or southeastern United States; they are vulnerable or imperiled in a few northern states.
The warmouth are good laboratory fish, small-sport fish, and the cane-pole fisherman catches it
for food.
CONTEXT AND CONTENT
Lepomis gulosus is from the Centrarchidae family, the second largest freshwater fish family of
the Perciformes order (Table 1). Lepomis is the largest Centrarchid genus with 12 species: L.
auritus, L. cyanellus, L. gibbosus, L. gulosus, L. humillis, L. macrochirus, L. marginatus, L.
megalotis, L. microlophus, L. miniatus, L. punctatus, and L. symmetricus.
Classification
Scientific Name
Meaning
Kingdom
Animalia
Phylum
Chordata
Class
Actinopterygii
ray-finned fishes
Order
Perciformes
perch-like
Family
Centrarchidae
sunfishes
Genus
Lepomis
scaled-gill cover
Species
gulosus
large mouth
Table 1. Warmouth classification, scientific name and meaning (Robins et al. 1991; Berra 2008)
GENERAL CHARACTERISTICS
The first and most obvious distinguishing feature of the warmouth is the redness of their eyes,
particularly in breeding males (Becker 1983). This, along with a propensity to frequent stump
fields, has earned them the nickname “red-eye stumpknocker” (Laerm and Freeman 1986). The
warmouth is likely given its name because its stripes resemble the warpaint of American Indians
(Moyle 1976). The fish’s aggressively hard strike, often breaking the surface of the water is
thought to be another reason for its name. Its large mouth extends to just beneath its large red
eyes lending itself to many of its other nicknames. Some of the warmouth’s common names are
bigmouth, Indian fish, sun trout, wood bass, goggle eye, red-eye bream, mud chub, perch mouth,
strawberry perch, weed bass, wide-mouth sunfish, yawnmouth perch, mudgapper, jugmouth,
molly, and morgan (Ross 2001).
Warmouth have deep bodies which are compressed laterally, similar to bluegill. The adult
warmouth have olive and mottled brown coloring, some have a purple tint and can change
coloring to blend in with surroundings. Their ventral side is gold in color. They range in length
from 10.2 to 25 cm long and can reach a typical weight of 1 kg, with the largest warmouth on
record caught in Florida weighing in at 1.1 kg (FFWCC 2013). Their mouth is terminal and
large. The upper jaw extends to the middle of the eye or farther with their lower jaw protruding
noticeably beyond their upper jaw, similar to bass (Mettee et al. 1996). They have a welldeveloped pad of lingual teeth and patches of teeth on the palatine bones (Ross 2001). Warmouth
also have teeth on their pterygoid (Hubbs et al. 1991; Hay 1894). They have sharp cone-shaped
teeth on both upper and lower jaws as well as similar, but more rounded, teeth on their lower
pharyngeal arches. On the side of their cheek, radiating from the eye and extending to the back
of the gill cover are three to four posterior reddish-brown streaks (Etnier 1993). One to two
anterior dark streaks radiates forward from their eye toward their mouth (Mettee et al. 1996).
Their supramaxilla bone’s length is greater than the width of maxilla. The opercular bone is
inflexible “to back margin and will usually fracture if bent forward” (Ross 2001).
DISTRIBUTION
Warmouth are naturally found in lentic or nearly lentic systems throughout much of the
eastern United States from the Great Lakes basins south to Florida and west across the Gulf
States to New Mexico (McMahon et al. 1984). They have also been introduced as far west as
California; however, they are not native to the area. They prefer clear-watered lakes and
large slow-moving streams with muddy bottoms and abundant aquatic vegetation for cover
(ODNR 2013). They can also be found in the Everglades of Florida as well as other marshes
in the southeastern US. (McMahon et al. 1984).
FORM AND FUNCTION
The warmouth is commonly confused with the green sunfish and the rock bass as they
possess striking similarities in both mouth and body size. Warmouth are, however,
generally larger than either of these (TPWD 2004). They are deep bodied and laterally
compressed though not as much as a bluegill, being more compressed dorsoventrally and
slightly less laterally. The warmouth also has three to four brown bars on its cheek and
teeth on its tongue where the green sunfish and rock bass both lack this tooth patch (Ross
2001). The rock bass is also identified as having five to seven anal spines as opposed to the
three to four spines on the warmouth (UWSGI 2013).
Warmouth have two dorsal fins, the first with 10 spines and the second with 9-10 soft rays;
however, they are joined together and appear as one. The anal fin has 3-4 spines and 8-10 soft
rays. The pelvic fin is thoracic, below the pectoral fin (Becker 1983). Fins have a darkly mottled
appearance. Pelvic fins contain melanophores. There is no adipose fin. They have 36-40 lateral
ctenoid scales (UWSGI 2013). The lateral line is complete and follows the anterior arch (Ross
2001).
Warmouth are easily sexed as the male warmouths are slightly larger than females and are
marked with an orange spot at the posterior termination of the dorsal fin (Larimore 1957). They
also have gold and/or light blue specks on their side. Breeding males will have more intense
coloring with an increase in the golden yellow colors along with bright red eyes.
ONTOGENY AND REPRODUCTION
They typically spawn in early spring; however, the breeding season of the warmouth begins in
March and can run until September. They may spawn two or more times a season (Laerm and
Freeman 1986). Unlike the other sunfish species, warmouth are solitary nesters. They do not
spawn in colonies (ODNR 2013). The male warmouth will use his caudal fin to fan the area he
wants the nest to create a bowl-shape nest. Their nest is built on gravel or rock in the shallows
near the water’s edge (Larimore 1957: Laerm and Freeman 1986). These nest sites are situated,
almost without exception, in very dense cover (Laerm and Freeman 1986). Warmouth perform
an intense courting ritual. The body of the male fish turns yellow and the redness of his eyes
deepens in hue. The male and female fish swim together in the center of the nest. The female
releases up to 63,200 eggs striking the male’s face with her body in the process. It is believed
that this action by the female signals the male to release his milt (Ross 2001). When spawning is
completed, the nest is guarded by the male until the hatchlings are ready to leave the nest (Laerm
and Freeman 1986). This usually occurs in a little over a week. After hatching, the warmouth fry
grow at a rate of 38 mm per year, assuming the presence of adequate resources. They will
become sexually mature in the second year of their seven-year lifespan (Laerm and Freeman
1986).
ECOLOGY
Migration.--Warmouth are typically a non-migratory species, traveling no more than 100 or so
miles for spawning or wintering. According to O’Connell and Vrancken (2010), during the year
following Hurricane Katrina, warmouth traveled approximately seven kilometers or 4.34 miles
downstream from Bayou Lacombe where their habitat had been destroyed and increased debris
had caused a decrease in dissolved oxygen levels. The warmouth requires an oxygen level of 3.6
ppm at 20 C but can survive for a short time in water with oxygen levels down to 1.0 ppm
(Larimore 1957). Even though dissolved oxygen levels had remained fairly stable downstream,
salinity levels and water temperatures were elevated and yet warmouth had migrated downstream
and had created new habitat and had increased abundantly during the year following Katrina
(O’Connell and Vrancken 2010). No warmouth were found upstream in the 2006 sampling.
Diet.--The warmouth is an invertivore/carnivore and more than other sunfish, tends towards
piscivory. It also feeds on aquatic insects and crustaceans (Cook 1959). At the larval stage the
primary source of food consists of small crustaceans such as copepods, ostracods and
cladocerans (Pflieger 1975). In a compilation of studies on warmouth 3.3-8.7 inches long, the
warmouth’s summertime diet consisted mainly of crayfish (Larimore 1957). The one autumn
study performed on warmouth
3 inches, diet consisted mainly of fish and mayflies (Larimore
1957). In warm water warmouth may consume 4% of its body weight in food per day (Hunt
1960). Warmouth rarely feed at any time other than the early morning (Larimore 1957). This can
render them more difficult to catch than other centrachids, though they will bite artificial lures
readily as well as angleworms, minnows, white grubs or crickets (Cook 1959).
BEHAVIOR
Social and hierarchal behavior.—Warmouth in a natural environment are not prone to
congregating in schools and therefore have little social hierarchy (Wallus 2008). Many fish form
groups in the winter but warmouth do not (Larimore 1957). Even though aggregation may occur
around the warmouths’ desire for similar cover or habitat and for a short period of time after
hatching, they are typically an independent unsociable species (Wallus 2008).
Feeding behavior.—The warmouth’s feeding activities involve seeking cover in rocks, stumps
or in aquatic vegetation where they hide and wait for prey to come by. They have a preference
for the shallows and along pond or river banks (Larimore 1957). They are sight feeders and use a
very simple process of hiding and waiting for food to dart by, and then they ambush their prey.
When the warmouth swiftly opens its large mouth, suction is created aiding in the capture of its
prey (Larimore 1957). Warmouth rarely eat motionless food and will often spend minutes
determining the acceptability of potential food before attacking it (Larimore 1957).
Learning behavior.—In a laboratory setting, the warmouth continued its independent behavior
even when learning. The secluded warmouth learned as quickly as the bluegill and more quickly
than the largemouth bass which worm was free as compared to which worm was on a hook (Witt
1949). When warmouth were placed in groups, it made more errors with the worms than either
the largemouth bass or the bluegill. Warmouth however were the slowest learners of all the
sunfish when presented artificial lures (Witt 1949).
Aggressive communication.--The warmouth typically has a quiet temperament and exhibits no
aggressiveness toward other fish except during nesting (Larimore 1957). When an intruder nears
the nest, male warmouth will puff out their opercles or gill plates to appear larger; during this
time, the intensity of his red eyes increase and his body turns a light golden color. As the intruder
nears, the warmouth will abruptly turn either up or to one side and will push small pulses of
water at the intruder with its tail (Larimore 1957). If this fails the warmouth will attempt to nip
the intruder. This nest-defending behavior is the same aggressive attitude the male uses in
courtship (Larimore 1957).
GENETICS
The warmouth was the lone species of the genus Chaenobryttus until recently when it was
determined the warmouth was “structurally” similar to and was capable of hybridizing with fish
of the genus Lepomis in the Centrarchid family (Becker 1983; Avis et al. 1977). The warmouth is
now regarded as a member of Lepomis. Warmouth have 24 pairs of chromosomes, with sex
chromosomes not likely to be differentiated from their autosomes (Childers 1968). The male
warmouth is thought to be the heterogametic sex with allele expression unencumbered (Childers
1985; Whitt el al. 1975). Hybridization is common between the warmouth and L. cyanellus
(greensunfish) and L. macrochirus (bluegill); these hybrids are only “partially fertile” (Childers
1968: Avis et al. 1977). The warmouth along with three other species of the genus Lepomis were
found to have “unique hemoglobin patterns in vertical starch gel electrophoresis” (Childers
1968). When hybridization occurred, the blood of bluegill/warmouth, greenfish/warmouth and
the warmouth/greenfish F1 hybrids, was found to have even greater gas transport attributes than
their parents thus creating “hybrid vigor” (Childers 1968). Hybridization with other Lepomis
within its habitat does not appear to be affecting the species health or survivability.
CONSERVATION
Distribution of warmouth is prevalent throughout the south and southeastern United States.
Warmouth are secure in Texas, Louisiana, Mississippi, Alabama, Oklahoma, Tennessee, North
Carolina, Virginia and Michigan. Populations in Arkansas, Georgia, Kansas, Kentucky, Indiana,
Ohio and Wisconsin are considered apparently secure. Populations in Pennsylvania and Illinois
are vulnerable. West Virginia populations are imperiled. Populations in Ontario Canada are
critically imperiled.
REMARKS
Economic aspect.--The economic importance of the warmouth comes from their popularity as
food and as a small sport fish, especially for the cane-pole fisherman (Larimore 1957). The
warmouth is an enjoyable species to catch as they have an aggressively hard strike, often
breaking the surface of the water. They are accessible with or without a boat, as they are easily
found in shallow water around trees, stumps and vegetation. They can be an excellent food fish
depending on the quality of their habitat and the accessibility of food.
Food fish.—Warmouth are excellent food fish if caught from a clean habitat with a plentiful
supply of prey. They have a similar taste and texture between a bluegill and a largemouth bass
(Larimore 1957). They can sometimes be small and bony and have a muddy flavor. This is why
habitat and a readily available supply of food are vital. Anglers often value the warmouth for
their gamy flavor and plump size (Larimore 1957).
Sport fish.—Warmouth can be a highly prized sport fish because it can be caught on a light rod
or pole and with artificial or live bait. Cane-pole fishermen have success with earthworms,
minnows, crickets, grasshoppers, grubs or just about any type of insect, hooked underneath a
pole float. Small artificial lures also work well on light rods, and warmouth have a particular
“gullibility” for artificial lures which makes it an attractive small-sport fish (Witt 1949).
Warmouth are also caught using a fly rod, especially in the spring (Becker 1983).
Because of its size, the warmouth is not considered a first rank sport fish, but the aggressiveness
the species use to attack its bait makes for an entertaining angling experience. Easy access to
warmouths’ shallow-water habitat provides everyone the opportunity to fish. The two pounders
will provide an excellent meal.
Lepomis gulosus as a laboratory fish.--Warmouth are good laboratory fish as they transport
well, are small enough for aquariums and large enough for handling. They tolerate low
dissolved oxygen levels, are a good biological assay species, have a quiet disposition, and feed
on a variety of, preferably live, food (Larimore 1957). Warmouth also have a relatively long
spawning season which allows for a variety of specimen sizes available throughout the
laboratory year. The warmouth have different individual and group learning behaviors from
other species within the Centrarchidae family (Larimore 1957). Most of all, they will nest and
spawn in a laboratory environment without being distressed by observers (Larimore 1957) and
typically live six to seven years (Mettee 1996).
The Lepomis gulosus artist.—One painting detailing all of the warmouth’s subtle differences
kept reoccurring throughout the warmouth research (Figure 1). Visual characteristics were easily
understood through the drawings of Duane Raver, who spent thirty years working for the North
Carolina Wildlife Resources Commission after graduating with a Fishery Management degree
from Iowa State in 1949 (Farlow 2009). Currently at 86, he continues to draw and paint after
years of studying his subjects. I have been in contact with him through the United States Postal
Service.
IMAGE
Figure 1. Typical adult warmouth (USFWS 2010).
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