Blue catfish

Appearance

Blue catfish are often misidentified as channel catfish. Blue catfish are heavy bodied, blueish gray in color, and have a dorsal hump. The best way to tell the difference between a channel catfish and a blue catfish is to count the number of rays on the anal fin. A blue catfish has 30–36 rays, whereas a channel catfish has 25–29. Blue catfish also have barbels, a deeply forked tail, and a protruding upper jaw.

Distribution

These large catfish have also been introduced in a number of reservoirs and rivers, notably the Santee Cooper lakes of Lake Marion and Lake Moultrie in South Carolina, the James River in Virginia, Powerton Lake in Pekin, Illinois, and Lake Springfield in Springfield, Illinois. This fish is also found in some lakes in Florida. The fish is considered an invasive pest in some areas, particularly the Chesapeake Bay. Blue catfish can tolerate brackish water, thus can colonize along inland waterways of coastal regions.

Status

The ability of the blue catfish to tolerate a wide range of climates and brackish water has allowed it to thrive in Virginia's rivers, lakes, tributaries, and the Chesapeake Bay. Unfortunately, the relatively low mortality rate, large body size, wide range of species preyed upon, and success as a predator has resulted in the blue catfish being considered a problematic invasive species in Virginia. Since their introduction in Virginia waters in the 1970s, blue catfish populations have exploded. Recent electrofishing studies have documented capture rates in excess of 6,000 fish/hr, whereas studies from the native range show peak electrofishing capture rates of 700 fish/hr. Clearly, blue catfish are a dominant species within the freshwater and oligohaline portions of Virginia's tidal rivers. The introduction of blue catfish in Virginia's tidal rivers was thought to have negative impacts on anadromous American shad, blueback herring, and alewife; however, predation of these species by blue catfish has been demonstrated to be minimal. Much of the narrative that has been built around the species as a dangerous apex predator in the Chesapeake Bay is simply not true. Researchers from Virginia Tech have found the species to be mostly herbivorous and omnivorous, with diets consisting largely of hydrilla and Asian clams, both of which are invasive to the Chesapeake Bay. Blue catfish do eat blue crabs with some regularity, which is problematic because blue crabs represent the most valuable fishery in the Chesapeake Bay.

Food

Blue catfish are opportunistic predators and eat any species of fish they can catch, along with crawfish, freshwater mussels, frogs, and other readily available aquatic food sources. Catching their prey becomes all the more easy if it is already wounded or dead, and blue catfish are noted for feeding beneath marauding schools of striped bass in open water in reservoirs or feeding on wounded baitfish that have been washed through dam spillways or power-generation turbines. Blue catfish are one of the only species of fish in the Mississippi river basin able to eat adult Asian carp.