Bluegill (Lepomis macrochirus) – Nonnative
Family Centrarchidae
Bluegill were first introduced to the Upper Delaware River as a sport fish due to 19th century stocking. They often inhabit ponds and lakes created by the construction of small dams in the Upper Delaware River’s tributaries but are also found in the river. Bluegill can reach 7.5 inches in length and can be distinguished from other sunfish because the black flap at the end of their gill cover contains no red spot. Spawning takes place during the summer from May to August. Males make depressions in the sand and gravel to serve as nests. Multiple females may contribute eggs to one nest, leading to as many as 60,000 fish produced from one nest. Males protect the eggs and young. Bluegill tend to be opportunistic feeders and commonly feed on aquatic plants and insects, crustaceans, and minnows.
Largemouth Bass
Evan Padua
Largemouth Bass (Micropterus salmoides) – Nonnative
Family Centrarchidae
Largemouth Bass was introduced to the Upper Delaware River as a sport fish and is today one of the most popular recreational sport fishes in the United States. The Largemouth Bass varies from bright to olive green with lighter colored sides and a splotchy black stripe down its side. Adults can reach 15 inches in length or more. Largemouth Bass prefer warmwater habitat with submerged aquatic vegetation. Spawning takes place in spring and early summer. Males make and defend a circular nest on gravel or sand. Females deposit the eggs, and then once they hatch, the males protect the young. The juveniles feed on zooplankton, insects, small fish, and may occasionally be cannibalistic. Adults feed on most frogs, crayfish, fish, and sometimes even ducklings.
Muskellunge
Kevin Corser
Muskellunge (Esox masquinongy) – Nonnative Family Esocidae
Muskellunge were first introduced to the Upper Delaware River along with other sport fishes during 19th century stocking. Muskellunge are large and quick growing fish with long and streamlined bodies. Their mouth superficially resembles a duckbill and is filled with sharp teeth. Muskellunge vary in color from greenish gray to yellow green or olive brown. The vertical dark bars running down the sides of muskellunge are more visible on younger fish but may fade with age. They prefer cool water and areas with an abundance of aquatic plants, which help them hide from prey. Muskellunge tend to be opportunistic and solitary predators. Their diet consists of mostly fish but given the chance they will also consume snakes, frogs, mice, and even water birds. Muskellunge spawn in the spring at nighttime and return to the same spawning site year after year. After females produce the eggs, they hatch in about 8-14 days. Young Muskellunge are at risk of predation by other fish, but soon growth large enough to start consuming fish themselves.
Redbreast Sunfish
Kevin Corser
Redbreast Sunfish (Lepomis auritus) – Native Family Centrarchidae
The Redbreast Sunfish is found in shallower portions of the Upper Delaware River. Their diet consists of small fish and crayfish, as well as other invertebrates and terrestrial insects that fall into the water. Redbreast Sunfish spend most of their life in one area, only moving during spawning season. Males construct the nests, which are grouped into closely packed colonies. They protect the nests, guarding the eggs and young after they hatch. Females can deposit around 3,300 eggs. Spawning takes place in spring and summer when the water temperature reaches around 68° F.
Rock Bass (Ambloplites rupestris) – Nonnative Family Centrarchidae
Rock Bass were introduced to the Upper Delaware River for sport fishing. Rock Bass are typically green to golden brown with dark mottling along their sides. Their eyes may be red or orange. Most Rock Bass grow to be 5 to 7 inches in length. Appropriately named, they prefer areas with rocks, stones, and boulder rubble. Spawning takes place in spring or summer. Males make circular shaped nests that they also defend, and females deposit an average of 5,000 eggs. Their diet consists of aquatic insects, crayfish, and fish.
Smallmouth Bass
Evan Padua
Smallmouth Bass (Micropterus dolomieu) – Nonnative Family Centrarchidae
Smallmouth Bass is a popular recreational fish species that was stocked in the Upper Delaware River in the late 1920s. The Smallmouth Bass has a bronze colored back with pale yellow sides, and 8 to 15 vertical olive colored bars on its sides. They prefer deep and rocky portions of the river that have a strong current. Spawning occurs in spring. Males build the nest, which is usually 14 to 30 inches in diameter. Several females contribute to one nest, and males guard the nest while the eggs begin hatching. Too high of water flow may be detrimental to Smallmouth Bass because it can cause the eggs to move downstream and perish. The diet of Smallmouth Bass consists of insect larvae, crayfish, and fish.
Walleye
Evan Padua
Walleye (Sander vitreus) – Nonnative Family Percidae
Throughout the 1920s and 1930s, Walleye was one of the most stocked fishes in the Upper Delaware River. Walleye range in color from bluish gray to olive-brown and golden yellow. They have a long body averaging around 22 inches in length with a forked tail. Walleye prefer cool and relatively deep water with a gravel, sand or rocky bottom. When females produce eggs, they are dispersed randomly and fall into spaces between rocks and gravel. Walleye spawn early in the spring and return to the same spawning site each year. Juveniles feed on zooplankton and then eventually switch to consuming fish, insect larvae, and even frogs. Walleye are adapted to feeding at dusk or nighttime; behind their retinas, they have a light reflective coating that allows them to see in dim lighting.
