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Bluegill
Bluegill (fish).jpg
Conservation status
Scientific classification
Synonyms

Lepomis purpurescens Cope, 1870

The bluegill (Lepomis macrochirus) is a species of freshwater fish sometimes referred to as "bream", "brim", "sunny", or "copper nose". It is a member of the sunfish family Centrarchidae of the order Perciformes. It is native to North America and lives in streams, rivers, lakes, and ponds. It is commonly found east of the Rockies. It usually hides around and inside old tree stumps and other underwater structures. It can live in either deep or very shallow water, and will often move from one to the other depending on the time of day or season. Bluegills also like to find shelter among aquatic plants and in the shade of trees along banks.

Bluegills can grow up to 12 inches (30 cm) long and about 4 12 pounds (2.0 kg). 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. The fish are omnivores and will eat anything they can fit in their mouth. They mostly feed on small aquatic insects and fish. The fish play a key role in the food chain, and are prey for bass, other (sunfish), northern pike, walleye, muskies, trout, herons, kingfishers, snapping turtles, and otters.

Summary

Bluegill sc
Bluegill from Lake Lanier, Buford, GA. (Caught & Released, June 14, 2004)

The bluegill is noted for the black spot (the "ear") that it has on each side of the posterior edge of the gills and base of the dorsal fin. The sides of its head and chin are commonly a dark shade of blue. The precise coloration will vary due to the presence of neurally controlledchromatophores 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 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 terminal mouth, ctenoid scales, and a lateral line that is arched upward anteriorly. The bluegill typically ranges in size from about four to 12 inches, and reaches a maximum size just over 16 inches. The largest bluegill ever caught was four pounds, 12 ounces in 1950.

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.

Distribution and habitat

Bluegill - Lepomis macrochirus from Rend Lake, IL
Male bluegill

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 and western New York. Today they have been introduced to almost everywhere else in North America, and have also been introduced into Europe, South Africa, Zimbabwe, Asia, South America, and Oceania. Bluegills have also been found in the Chesapeake Bay, indicating they can tolerate up to 1.8% salinity.

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, 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 has wreaked havoc with native species, especially in Lake Biwa in Shiga Prefecture. The Daijō Tennō has since apologized.

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's underwater. They can often be found around weed beds, where they search for food or spawn. 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 60 to 80 °F (16 to 27 °C), and tend to have a home range of about 320 square feet (30 m2) 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. Bluegill are usually found in schools of 10 to 20 fish, and these schools will often include other panfish, such as crappie, pumpkinseeds, and smallmouth bass.

Ecology

Young bluegills' diet consists of rotifers and water fleas. The adult diet consists of aquatic insect larvae (mayflies, caddisflies, dragonflies), but can also include zooplankton, shrimp, crayfish, leeches, snails, and other small fish. 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, trout, muskellunge, turtles, northern pike, yellow perch, walleye, catfish, and even larger bluegill. Herons, kingfishers, and otters have also been witnessed catching bluegill in shallow water. However, the shape of the fish makes them hard to swallow. Raccoons are also believed to be among their predators.

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.

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. Backward swimming in the bluegill is more complex than steady swimming, as it is not just the reversal of forward swimming. The fish utilizes its pectoral fins to provide a rhythmic beat while the dorsal and anal fins produce momentum to drive the fish backwards. The pectoral fins' rhythmic beat is asymmetric and aids the fish's balance in its slow, backward movement.

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.

Relationship with humans

The bluegill is the state fish of Illinois.

Fishing

AlabamaFarmPondBlueGill
Bluegill caught in an Alabama pond

Bluegills are popular panfish, caught with live bait such as worms, crickets, grasshoppers, flies, 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.

Fishermen are sometimes able to use polarized sunglasses to see through water and find bluegills' spawning beds. Bluegill have a rather bold character; many have no fear of humans, eating food dropped into the water, and a population in Canada's Lake Scugog will even allow themselves to be stroked by human observers. Because of their size and the method of cooking them, bluegills are often called panfish.

The IGFA all tackle world record for the species stands at 2.15 kg (4 lb 12oz) 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.

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.

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