Bony Fishes (Osteichthyes)

• Bony fish (Osteichthyes) are the most successful and abundant of the 2 groups of fishes (96% of all fish; ~27,000 species)

• Osteichthyes possess a hard, strong - but lightweight - skeleton made of calcium that supports them and is responsible for their success (and diversity) as a group

• Bony fish include tuna, cod, flounder, goldfish, and other familiar species

Bony Fishes (Osteichthyes)

• The composition of their skeleton is not the only distinguishing feature of bony fishes

• In contrast to the tiny, pointed placoid scales of cartilaginous fishes, bony fish usually have cycloid or ctenoid scales, which are thin, flexible, and overlapping– Cycloid scales have a smooth outer edge– Ctenoid scales have a toothed outer edge

Bony Fishes (Osteichthyes)

• The scales are made of bone and are covered by a thin layer of skin and a protective mucus

• Bony fish are also characterized by the presence of a gill flap, or operculum

Bony fish have a bony opeculumCartilaginous fish have gill slits

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Bony Fishes (Osteichthyes)

• Bony fish are subdivided into two major groups– Lobe-finned fishes– Ray-finned fishes

• Lobe-finned fishes are largely extinct, but include lungfishes and coelacanths

• Ray-finned fishes, in contrast, are far more successful, and can be further divided into soft-rayed and spiny-rayed bony fish

Soft-rayed vs. Spiny-rayed

• Soft rayed fish representatives include:– Cod– Trout– Herring

• Spiny-rayed fish representatives include:– Bass– Groupers– Reef fish