Bluegill, Lepomis macrochirus

The Bluegill, Lepomis macrochirus, whose common Spanish name is mojarra oreja azul, is a member of the Sunfish or Centrarchidae Family, known collectively as lobinas in Mexico. Globally, there are thirteen species in the genus Lepomis, seven of which are found in the streams, rivers, lakes, and ponds of Mexico’s freshwater systems.

The Bluegills have very deep and highly compressed bodies. They are mainly olive-green dorsally and transition to yellowish ventrally. They have an iridescent blue and purple region on their gill cover which gives rise to their common name. They also have a dark smudge at the base of their dorsal fin and six to eight very subtle olive-colored bars on their sides. The breasts of breeding males are bright orange. Juveniles are much paler than adults. They have a short head and a very small terminal mouth. Their anal fin has 3 spines and 10 to 12 rays; their caudal fin is slightly forked and rounded; their dorsal fin is continuous with 6 to 13 spines and 12 to 13 rays; and their pectoral fin has 12 or 13 rays. Their lateral line arches upward anteriorly. They are covered with small scales.

The Bluegills are found in virtually all slow-moving freshwater systems in North America. They reach a maximum length of 41 cm (16 inches) and weight of 2.2 kg (4.85 pounds). They prefer water with many aquatic plants and hide within fallen logs or water weeds. They also prefer water temperature between 16oC (60oF) and 27oC (80oF) and will migrate accordingly. They are normally found in schools of 10 to 20 individuals and these schools often include various other panfish. They have a very small home range, which measures about 320 square feet. They can tolerate heat and salinity but avoid direct sunlight. They are omnivores and non-selective feeders and their diet includes small aquatic insects and fish. They feed during daylight hours predominantly between dawn and dusk. They consume approximately 5% of their body weight per day when active. They are an important prey for larger fish including Brown Trout, Largemouth Bass, Muskies, Striped Bass, and Walleye. They are also preyed upon by sea birds and otters, raccoons, and turtles. They rely on their ability to outmaneuver their attackers to avoid predation and are also difficult to swallow due to their body shape. Reproduction is oviparious and polygynandrous (promiscuous) and occurs continually when water temperatures are in excess of 20oC (70oF). During this period males become highly territorial and highly aggressive. They build highly visible nests in very shallow sand bottoms; these nests are about 12 inches in diameter and found in clusters of up to 50 beds together. Each female, based on size, will deposit between 1,000 and 100,000 eggs into the nest. Fertilization is external and males remain on the nest until the eggs hatch in approximately 5 days and the fry swim away on their own. Young fish feed on plankton, but as they grow their diet shifts to aquatic insects and insect larvae. With high reproductive rates, low predation, and low fishing pressure, Bluegill population growth can be explosive. One of the great recreational angling experiences I have had is Bluegill fishing with a fly rod and a small popper when they “are on the bed” in the spring in Lake Okeechobee, Southern Florida. Bluegills grow rapidly in their first three years. They have a lifespan of five to eight years in the wild and up to 11 years in captivity.

Bluegills are found throughout North America ranging from Québec to northern Mexico and are most likely moving toward southern Mexico as we speak. They are the State Fish of Illinois.

The Bluegill is most likely confused with the Orangespotted Sunfish, Lepomis humilis and the Redear Sunfish, Lepomis microlophus, but both lack the distinct spot at the base of their soft dorsal fin.

Bluegills are abundant in their native range but have been raised by aquaculture and widely transplanted, therefore are now the most common recreational freshwater fish in North America. They are considered an excellent species for teaching angling to children. They are caught at dawn and dusk with very small hooks on live bait, flies, white bread, corn kernels, hot dogs, raw chicken, or lures. Pound for pound they put up an excellent fight. They are also considered an excellent food fish. They are stocked in rivers and lakes as food for Largemouth Bass. They are used on occasion as live bait for Blue Catfish, Flathead Catfish, and Largemouth Bass. Bluegills are also a major invasive pest causing overcrowding conditions and destroying native populations; they have been banned from commercial trade in Germany and Japan. They are currently used by the cities of New York, San Francisco, and Washington to monitor freshwater for the presence of pollutants and toxins such as cyanide, fuel spills, heavy metals, mercury, pesticides, and phosphates. Bluegills cough by flexing their gills to expel unwelcome materials from their breathing passages. The frequency of these coughs can be monitored by sensitive listening devices giving an indication of current water quality. In their native range they are considered an important asset to pond and lake management by keeping crustacean and insect populations under control.

Bluegill (1)Bluegill, Lepomis macrochirus, Juvenile. Fish caught on a fly rod out of an irrigation pond in the greater Los Cabos area, Baja California Sur, August 2008. Length: 18.0 cm (7.1 inches). Catch courtesy of Eduardo Correa, Mexico City, Mexico.