Bluegill
The bluegill, sometimes referred to as "bream", "brim", "sunny", or, in Texas, "copper nose", is a species of North American freshwater fish, native to and commonly found in streams, rivers, lakes, ponds and wetlands east of the Rocky Mountains. It is the type species of the genus Lepomis, from the family Centrarchidae in the order Centrarchiformes.
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 aquatic insects and baitfishes. The fish are important prey for bass, other larger sunfish, northern pike and muskellunge, walleye, trout, herons, kingfishers, snapping turtles and otters, and play a key role within the food chain of its freshwater ecosystem.
A popular panfish among anglers, bluegill usually hide around and inside old tree stumps in swamps and other underwater structures, and can live in either deep or very shallow water. Bluegills also like to find shelter among aquatic plants 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 on each side of the posterior edge of the gill covers 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 chromatophores 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 terminal mouth, ctenoid scales, and a lateral line that is arched upward anteriorly.The bluegill typically ranges in size from about, and reaches a maximum size just over. The largest bluegill ever caught was 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.
Potential subspecies
Bluegills are sometimes split into three subspecies, although their validity is contested. This includes the northern bluegill, the coppernose bluegill, and the southwestern bluegill.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, 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 wreaked havoc with native species, especially in Lake Biwa. Akihito 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 that is under water. 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, 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. 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, copepods, water fleas, and insects. The adult diet consists of aquatic insect larvae, but can also include terrestrial insects, zooplankton, shrimp, crayfish, leeches, other worms, 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. 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 when the fish comes into contact with its environment. In standard swimming the bluegill sunfish relies on its caudal 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.
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. The caudal fin is a main source of momentum in typical kinematic models of the C-start escape response but the bluegill draws a majority of its momentum from the body bending associated with the response, as well as its dorsal and anal fins. The dorsal and anal fins' roles as propulsors during escape response suggest that the size of the fins could lead to an evolutionary advantage when escaping predators.