Blackfish is a term used to describe several types of fish and two types of cetaceans. Fish commonly referred to by the term include the Alaska blackfish, the Sacramento blackfish, and the river blackfish. The melon-headed whale and the killer whale, also known as an orca, are also referred to by this name.
The Alaska blackfish, Dallia pectoralis, is a cylindrical fish that is olive brown in coloring. The fish has four to six dark spots that run vertically down its side, and it has a white belly. The fins have red-brown speckles. Reaching lengths of 7 inches (17.7 cm), the fish are found in Alaska and the islands of the Bering Sea.
The Sacramento blackfish, Orthodon microlepidotus, is found in central California. This fish is the only member of the genus Orthodon. Dark in color over its entire body, the fish is lighter as a juvenile and grows darker as it matures. Growing to lengths of 21.5 inches (55 cm), the fish is common in the Sacramento and San Joaquin Rivers. They are also found in the waters that run into the San Francisco Bay.
The River blackfish, Gadopsis marmoratus, is found in the fresh water of Australia’s Murray-Darling river system from Queensland to Victoria. A nocturnal carnivore, the fish’s diet consists of crayfish, shrimp, and other small fish. Reaching lengths of 11.8 inches (30 cm), the fish are in decline because of overfishing, competition from introduced species, and siltation of streams.
The melon-headed whale, Peponocephala electra, is sometimes referred to as the many-toothed blackfish or the electra dolphin. This whale is part of the dolphin, or Delphinidae, family. The entire family is often called by the common name blackfish. The killer whale, Orcinus orca, is also part of this family.
The melon-headed whale is found in most of the world’s tropical waters. The body of the whale is light gray, and the face, which is a rounded cone-shape, is dark gray. Reaching lengths of 10 feet (3 m), the primary diet of the melon-headed whale is squid.
The killer whale is the only species in the genus Orcinus. With a black back, white sides, and a white chest, the killer whale has a white patch above and behind the eye. Calves have a yellowish tint that fades to white. Male killer whales average 20 to 26 feet (6 to 8 m) in length, and females are 16 to 23 feet (5 to 7 m).