Monofin Dartfish

Ptereleotris monoptera

The Monofin Dartfish, known scientifically as Ptereleotris monoptera, is a small, elongated reef fish that can grow up to 12 cm in length. It is characterized by its pale blue to yellowish coloration, with a distinctive broad area of deeper blue on the upper abdomen. A notable feature is the broad, blackish bar extending from the eye onto the chin. Its dorsal fin is continuous, with the spinous part being lower than the soft portion, and it has a unique chin with a fleshy protuberance. The scales of the Monofin Dartfish are very small, fully embedded, and well separated, contributing to its sleek appearance. This species is found in the Indo-Pacific region, ranging from the Seychelles and Chagos Islands to the western Pacific. It inhabits reef-associated environments, typically residing at depths between 6 and 50 meters, though most commonly found between 6 and 15 meters. The Monofin Dartfish prefers habitats that include rubble and can often be seen in pairs, living in burrows situated in coral rock or sand. The Monofin Dartfish is monogamous and feeds primarily on zooplankton. Divers may encounter these fish forming large, though diffuse, colonies. Such aggregations may be influenced by ecological factors like substrate type, current patterns, and water depth. The species is assessed as Least Concern on the IUCN Red List and is harmless to humans.