Regalecus

Regalecus is a genus of oarfish. These are large, elongated, pelagic, deep-sea fish that make up the family Regalecidae. The name Regalecus comes from the Latin word regal, meaning royal, likely referring to the fish's appearance. There are two recognized species in the genus: Regalecus glesne, commonly known as the Atlantic oarfish or King of the Herrings, and Regalecus russelii, the Pacific oarfish.

These fish are characterized by their ribbon-like bodies, which can grow to extraordinary lengths, making them among the longest bony fish in the world. While precise measurements are difficult due to their elusive nature and tendency to be found deceased or damaged, individuals exceeding 10 meters (33 feet) have been reported, with some estimates suggesting lengths up to 17 meters (56 feet). Their bodies are laterally compressed and lack scales, instead possessing a tough, leathery skin. A distinctive feature is their prominent dorsal fin that runs the entire length of their body, with a crest of reddish, elongated rays at the head. Their coloration is typically silvery with iridescent blue or green hues, and they often have red fins.

Regalecus are rarely seen, as they inhabit the mesopelagic to bathypelagic zones of the world's oceans, typically found at depths between 200 and 1,000 meters (660 to 3,300 feet). They are believed to be solitary creatures. Their diet is thought to consist mainly of small crustaceans, krill, and small fish, which they likely filter from the water. Due to their deep-sea habitat and infrequent sightings, much of their behavior and life cycle remains poorly understood. Sightings are often a result of dead or dying specimens washing ashore or being caught accidentally in fishing nets.