Opistognathidae

Jawfishes, known scientifically as Opistognathidae, belong to the order Blenniiformes and include roughly 80 species. They live in warmer waters of the Atlantic, Pacific, and Indian Oceans, ranging from shallow areas down to a few hundred meters deep. Their taxonomy is complicated, with several species still undescribed.

These fish resemble blennies in appearance. Most are small, elongated creatures that grow up to 10 cm (3.9 in), though a few, like the giant jawfish (Opistognathus rhomaleus), can reach about 0.5 m (1 ft 8 in). They have large heads, mouths, and eyes relative to their bodies. A single, long dorsal fin with 9 to 12 spines runs along their back, and their caudal fin may be rounded or pointed.

Jawfishes are known for digging burrows in sandy seabeds. They fill their mouths with sand and spit it elsewhere, slowly carving out a tunnel. From the safety of these burrows, they hover and feed on plankton or small organisms, darting back inside at any hint of danger. They defend the territory around their homes.

Except for the blue-spotted jawfish (Opistognathus rosenblatti), all jawfishes are mouthbrooders: they hold their eggs in their mouths until they hatch, shielding the fry from predators. The gestation period varies by species; for example, the gold-specs jawfish (Opistognathus randalli) typically keeps its clutch for 8 to 10 days before hatching.