The Horse-head Fish, commonly known as the Greenfin Horse-faced Filefish (Thamnaconus septentrionalis), is a marine species belonging to the family Monacanthidae. It is widely found in the coastal waters of the western Pacific Ocean, including regions such as Japan, China, Korea, and Taiwan. This fish is named for its distinctive head shape, which resembles that of a horse, and its elongated, laterally compressed body.

Typically, the Horse-head Fish grows to around 30 to 50 centimeters in length. Its coloration varies from olive green to brownish hues, often with subtle patterns that help it camouflage among seaweed and rocky reefs. The species feeds primarily on algae, small invertebrates, and sometimes sponges, playing an important ecological role in maintaining reef health.

Due to its firm, white flesh and mild flavor, the Horse-head Fish is valued in regional cuisines. It is often prepared through steaming, simmering, or frying, and is sometimes served as sashimi in Japan. The texture is tender yet resilient, suitable for various cooking methods, and its subtle taste pairs well with light seasonings.

Though not as internationally known as other fish species, the Horse-head Fish holds a niche culinary and cultural significance in East Asian coastal communities. Its seasonal availability and unique texture contribute to its popularity in local markets and traditional dishes. Additionally, sustainable fishing practices have become increasingly important to preserve its populations and marine habitats.