Threefin blennyTripterygiidae

Threefin blennies (Tripterygiidae) are diminutive marine fishes with slender, blennioid-like bodies. They typically reach up to 6 centimetres (2.4 inches) in length. A key characteristic is their tripartite dorsal fin, from which their common and scientific names derive (Greek 'tripteros' meaning 'three wings'). The first two segments of this fin are spinous. They also possess notably large pectoral fins and diminutive pelvic fins, each with a single spine, situated beneath the gills. Many species display vivid coloration, often for camouflage, and males frequently exhibit more pronounced colours or elongated second dorsal fins.

These demersal fish inhabit shallow, sunlit reef environments, typically from the surface down to 30 metres (100 feet). They are found in lagoon systems and on seaward reef slopes, living on coral formations and rocky outcrops. Threefin blennies are diurnal and territorial, feeding on small invertebrates. When disturbed, they retreat into rocky cavities or crevices.