The bluegill ( Lepomis macrochirus), sometimes referred to as "bream", "brim", "sunny", or, in Texas, "copper nose",
Bluegills can grow up to long and about . While their color can vary from population to population, they typically have a very distinctive coloring, with deep blue and purple on the face and gill cover, dark olive-colored bands down the side, and a fiery orange to yellow belly. They are omnivorous and will consume anything they can fit in their mouth, but mostly feed on small and . The fish are important prey for bass, other larger Centrarchidae, northern pike and muskellunge, walleye, trout, herons, kingfishers, snapping turtles and otters, and keystone species within the food chain of its freshwater ecosystem.
A popular panfish among Angling, bluegill usually hide around and inside old tree stumps in and other underwater structures (e.g. snags), and can live in either deep or very shallow water. Bluegills also like to find shelter among and in the shade of trees along banks, and will often move from one cover to another depending on the time of day or season.
Description
The bluegill is noted for the large black appendage (the "ear") on each side of the posterior edge of the
as well as the base of the dorsal fin. The sides of its head and chin are commonly a dark shade of blue, hence the name "bluegill". The precise coloration will vary due to the presence of neurally controlled
under the skin.
The fish usually displays 5–9 vertical bars on the sides of its body immediately after being caught as part of its threat display.
It typically has a yellowish breast and abdomen, with the breast of the breeding male being a bright orange.
The bluegill has three anal fin spines, ten to 12 anal fin rays, six to 13 dorsal fin spines, 11 to 12 dorsal rays, and 12 to 13 pectoral rays. They are characterized by their deep, flattened bodies. They have a
fish jaw,
ctenoid scales, and a
lateral line that is arched upward anteriorly.
[Sublette, J. E., M. D. Hatch, and M. Sublette. 1990. University of New Mexico Press, Albuquerque. 393 pp]
The bluegill typically ranges in size from about , and reaches a maximum size just over . The largest bluegill ever caught was in 1950.[Ross, S. T. 2001. The Inland Fishes of Mississippi. University Press of Mississippi, Jackson. 624 pp]
The bluegill is most closely related to the orangespotted sunfish and the redear sunfish, but different in a distinct spot at or near the base of the soft dorsal fin.
Potential subspecies
Bluegills are sometimes split into three subspecies,
although their validity is contested.
This includes the northern bluegill (
L. m. macrochirus), the coppernose bluegill (
L. m. purpurascens), and the southwestern bluegill (
L. m. speciosus).
Distribution and habitat
The bluegill occurs naturally in the
United States east of the
Rocky Mountains from coastal
Virginia to
Florida, west to
Texas and northern
Mexico, and north to western
Minnesota, New York and southeastern
Ontario.
They have been introduced widely in
North America and
Europe,
South Africa,
Zimbabwe,
,
South America, and
Oceania. Bluegills have also been found in the
Chesapeake Bay, indicating they can tolerate up to 1.8% salinity.
[Schultz, Ken. Ken Schultz's Field Guide to Freshwater Fish. Hoboken, NJ: J. Wiley & Sons, 2004]
In some locations where they have been transplanted, they are considered pests: trade in the species is prohibited in Germany and Japan. In the case of Japan, bluegills were presented to the then-crown prince, Emperor Akihito, in 1960 as a gift by Richard J. Daley, mayor of Chicago. The prince, in turn, donated the fish to fishery research agencies in Japan, from which they escaped and became an invasive species that wreaked havoc with native species, especially in Lake Biwa. Akihito has since apologized.[McCurry, Justin (November 26, 2007). "Japan in culinary offensive to stop spread of US fish". The Guardian.]
Bluegill live in the shallow waters of many lakes and ponds, along with streams, creeks, and rivers. They prefer water with many aquatic plants, and seclude themselves within or near fallen logs, water weeds or any other structure (natural or manmade) that is under water. They can often be found around weed beds, where they search for food or spawn.[Lee, D. S. 1980. Lepomis macrochirus (Rafinesque 1819), Bluegill. pp. 597 in D. S. Lee, et al. Atlas of North American Freshwater Fishes. N. C. State Mus. Nat. Hist., Raleigh, 854 pp] In the summer, adults move to deep, open water where they suspend just below the surface and feed on plankton and other aquatic creatures. Bluegill try to spend most of their time in water from , and tend to have a home range of about during nonreproductive months. They enjoy heat, but do not like direct sunlight – they typically live in deeper water, but will linger near the water surface in the morning to stay warm.[Paulson, Nicole, and Jay T. Hatch. "Fishes of Minnesota – Bluegill." GC 1112 Welcome. Minnesota Department of Natural Resources, 18 June 2004. Web. 04 May 2011.]
Ecology
Young bluegills' diet consists of
rotifers,
copepods,
, and
insects (mainly
Chironomidae).
The adult diet consists of aquatic insect larvae (
mayflies,
caddisflies,
dragonflies), but can also include terrestrial insects,
,
,
,
leeches, other
,
, and other small fish (such as
minnows).
[Carlander, K.D. 1997. Handbook of freshwater fishery biology. Volume 2. Life history Data on centrarchid fishes of the United States and Canada. Iowa State Univ.Press, Iowa.] If food is scarce, bluegill will also feed on aquatic vegetation and
algae,
and if scarce enough, will even feed on their own eggs or offspring. As bluegill spend a great deal of time near the surface of water, they can also feed on surface bugs. Most bluegills feed during daylight hours, with a feeding peak being observed in the morning and evening (with the major peak occurring in the evening).
Feeding location tends to be a balance between food abundance and predator abundance. Bluegill use
gill rakers and bands of small teeth to ingest their food. During summer months, bluegills generally consume 3.2 percent
of their body weight each day. To capture prey, bluegills use a suction system in which they accelerate water into their mouth. Prey comes in with this water. Only a limited amount of water is able to be suctioned, so the fish must get within 1.75 centimeters of the prey.
In turn, bluegill are prey to many larger species, including largemouth bass, smallmouth bass, striped bass,
Adaptations
Bluegills have the ability to travel and change directions at high speeds by means of synchronized fin movements. They use notched caudal fins, soft
dorsal fins, body undulations, and
pectoral fins to move forward. Having a notched caudal fin allows them to accelerate quickly. The speed of their forward motion depends on the strength of which they abduct or adduct fins. The flat, slender body of the bluegill lowers water resistance and allows the bluegills to cut effectively through water. The large, flexible pectoral fins allow the fish to decelerate quickly. This superior maneuverability allows the bluegill to forage and escape predators very successfully. Bluegills have a
lateral line system, as well as inner ears, that act as receptors for vibration and pressure changes. However, bluegills rely heavily on sight to feed, especially in their foraging. Optimal vision occurs in the daylight hours. The mouth of the bluegill is very small and requires the use of the pharynx to suck in prey.
[Swingle, H. S. and E. V. Smith. 1943. Factors affecting the reproduction of bluegill bream and large black bass in ponds. Ala. Poly-Tech. Inst. Agr. Exp. Stn. Circ. 87:8]
Standard and backward swimming
The bluegill sunfish relies heavily on the flexibility of its fins to maintain maneuverability in response to fluid forces. The bluegill's segmentation in its pectoral fin rays mitigates the effects of fluid forces on the fish's movement.
The bluegill has a variety of unusual adaptations that allow it to navigate different environments. In conditions where the bluegill is deprived of its various sensory abilities, it utilizes its pectoral fins in navigation.
If the bluegill's visual input or lateral line input were to be compromised, its pectoral fins are then able to be utilized as mechanosensors
through the bending of the fin(s) when the fish comes into contact with its environment.
In standard swimming the bluegill sunfish relies on its caudal (tail) fin, dorsal fin, and anal fin.
The bluegill's caudal fin muscles are important in the fish's slow swimming and also important in the beginning stages of the fish increasing its swimming speed.
The dorsal and anal fins are two types of median fins that work in parallel to balance torque during steady swimming.
When swimming backwards, the bluegill utilizes a plethora of fin muscles located in various parts of its body.
C-start escape response
The bluegill, amongst a wide array of other fishes,
exhibits the C-start escape response, which is generated by large neurons called
Mauthner cells.
Mauthner cells operate as a command center for the escape response and respond quickly once the neural pathway has been activated by an initial stimulus.
The cells trigger a contraction of muscle that bends the fish body into a 'C' to then aid in the propulsion away from a predator.
The C-start trajectory is highly variable, allowing the fish to alter its escape response each time.
Because of this high variability, predators have a lower chance of learning a successful predation technique to capture the fish.
The C-start escape response produces other advantages, including the ability to move quickly and unpredictably to capture prey.
Hydrodynamically, the bluegill exhibits specific flow patterns that accompany its C-start escape response.
Reproduction and lifestyle
Spawning season for bluegills starts late in May and extends into August. The peak of the spawning season usually occurs in June in waters of . The male bluegills arrive first at the mating site. They will make a spawning bed of six to 12 inches in diameter in shallow water, clustering as many as 50 beds together. The males scoop out these beds in gravel or sand. Males tend to be very protective and chase everything away from their nests, especially other male bluegills. Some bluegills, regardless of their small size, will even attack snorkelers if they approach the edge of the nest. As a female approaches, the male will begin circling and making grunting noises. The motion and sound of the males seem to attract the females. Females are very choosy and will usually pick males with larger bodies and "ears", making larger size a desirable trait for males to have. If the female enters the nest, both the male and female will circle each other, with the male expressing very aggressive behavior toward the female. If the female stays, the pair will enter the nest and come to rest in the middle. With the male in an upright posture, the pair will touch bellies, quiver, and spawn. These actions are repeated at irregular intervals several times in a row. Once the spawning is done, the male will chase the female out of the nest and guard the eggs.
The
fertilization process is entirely external. The male's sperm combines with the female's eggs in the water. Smaller males will often hide in nearby weeds and dart into the nest as they attempt to fertilize the eggs. They then quickly dart away.
The size of the female plays a large role in how many eggs will be produced. A small female can produce as few as 1,000 eggs, and a large, healthy female can produce up to 100,000 eggs. The male continues to watch over the nest until the
larvae are able to hatch and swim away on their own. The bluegill generally begins its spawning career at one year of age, but has been found to spawn as early as four months of age under favorable conditions.
[Sternberg, Dick. Freshwater Gamefish of North America. 1987.] Anglers find spawning season to be a very successful time to fish for bluegills, as they aggressively attack anything, including a hook, that comes near.
The growth of the bluegill is very rapid in the first three years, but slows considerably once the fish reaches maturity. Many fish reach five to eight years old, and in extreme cases, can live 11 years.
Hybridization with other species
Occasionally a bluegill may spawn with another member of its genus, though this is rare. This tends to happen in bodies of water that are fairly isolated and have a decent population of bluegill in close proximity to another, smaller, population of lepomid species such as
green sunfish. Limited nesting grounds can also factor in hybridization causing the females of one species to prefer the nest of another.
Bluegill can theoretically hybridize with all other species in the genus
Lepomis, though the most common hybrid is the greengill.
The hybrid fish are aggressive and have larger mouths than their bluegill parent. These fish also grow faster than other small mouth fish due to its bigger mouth. Greengills or hybrid bluegills are the most efficient in growth and can reach approximately 2 lbs or 0.91 kg in one year.
By artificially stripping and fertilizing eggs, bluegills can hybridize with centrarchid species outside of the genus Lepomis, creating intergeneric hybrids. In this manner, bluegills have been crossed with black crappie ( Pomoxis nigromaculatus) and largemouth bass ( Micropterus salmoides).
Relationship with humans
The bluegill is the
state fish of
Illinois.
At Lake St. Helen, Michigan, an annual "Blue Gill Festival" is held in July.
Fishing
Bluegills are popular
panfish, caught with live bait such as worms, crickets, grasshoppers,
fly fishing, minnows, maggots or small frogs, as well as small shrimp bits, processed bait, bread, corn, other table scraps,
small crankbaits, spinners, fake worms, or even a bare hook. They mostly bite on vibrant colors like orange, yellow, green, or red, chiefly at dawn and dusk. They are noted for seeking out underwater vegetation for cover; their natural diet consists largely of crickets, water bugs,
larvae, and very small fish. The bluegill itself is also occasionally used as bait for larger game fish species, such as
blue catfish,
flathead catfish and
largemouth bass.
[Coble, Daniel W. "Effects of Angling on Bluegill Populations: Management Implications." North American Journal of Fisheries Management 8.3 (1988): 277]
Fishermen are sometimes able to use polarized sunglasses to see through water and find bluegills' spawning beds.[ "Fishes of Minnesota: Bluegill Minnesota DNR." Minnesota Department of Natural Resources: Minnesota DNR. Web. 04 May 2011.]
The IGFA all tackle world record for the species stands at 2.15 kg (4 lb 12 oz) caught from Ketona lake in Alabama in 1950.
Management
Bluegill populations are notably vulnerable to effects of angling and harvest, particularly in size-structure.
Large males appear to be especially vulnerable to effects of fishing because of their tendency to guard nests in the center of colonies.
Populations with large males are increasingly difficult to find, and are usually only found in remote locations without angling pressure
or in more southern regions where growth rates are high. Reduced bag limits appear to show potential for improving size-structure in over-fished populations.
In a 1973 study reported by the EPA, the waterborne administration of 180 ppm of calcium propionate was found to be slightly toxic to bluegill.
Bluegills play an important role in pond and lake management to keep crustacean and insect populations low, as a single bluegill population may eat up to six times its own weight in just one summer.
