The gender of male and female blue catfish can be determined by the distinctive humps that appear on the backs of the males between the dorsal fins and the head. The females are more streamlined and can reach any size, but the males start developing these distinctive humps once they reach 10 pounds. The males also have more rounded heads.
Although blue catfish reach up to 150 pounds with a maximum length of 5.4 feet, they average closer to 20 to 40 pounds. Their backs and upper sides are pale blue, olive or gray with white chins. Their fins are bordered in black. The male and female build a nest together for their eggs, communally caring for them until the young are 2 to 4 inches long. Adults eat mayflies, crayfish, clams and other fish, while juveniles eat zooplankton. Common in North America, blue catfish can be found in Mississippi, Missouri, Ohio, Mexico and parts of Guatemala at depths up to 164 feet. Blue catfish feed primarily at night. The blue catfish is sometimes confused with the channel catfish, but it can be distinguished by the straight edge of the anal fin, as opposed to the channel catfish's convex edge.