Rex Sole

The rex sole is a right-eyed flatfish in the family Pleuronectidae, found in the northeastern Pacific Ocean from the Bering Sea to Baja California. It is a slender, elongated species closely related to the Atlantic witch flounder, and it typically lives in deeper, colder waters than many nearshore Pacific flatfish. Rex sole have unusually long pectoral fins for a flatfish, and their thin, delicate bodies distinguish them from bulkier Pacific species such as petrale sole or California halibut. The species is caught incidentally in deeper continental shelf and slope trawl fisheries along the West Coast and is monitored as part of regional groundfish stock assessments.

• Long, narrow, elongated body, thinner than most other Pacific flatfish
• Eyes on the right side of the head
• Upper side is uniform light brown to grayish-brown, typically without bold markings
• Notably long pectoral fin on the eyed side, often nearly as long as the head
• Small mouth relative to body size
• Adults typically reach 25-40 cm, with large individuals to 50 cm

Its slender shape and unusually long pectoral fin distinguish it from Dover sole and petrale sole, which have shorter fins and comparatively deeper bodies.

Rex sole occur along the northeastern Pacific coast from the Bering Sea south to Baja California. They inhabit sandy or muddy seafloor on the outer continental shelf and upper slope, typically at depths of about 30 to 800 meters, with adults generally concentrated in the deeper part of this range. The species favors cooler, darker deep-shelf waters and is less commonly encountered in shallow nearshore habitat compared to many other Pacific flatfish. Its distribution overlaps broadly with other deep-shelf groundfish, and stable, muddy-sand substrate along the shelf edge appears to be the key habitat requirement.

Rex sole are demersal fish that forage along soft seafloor for small invertebrates such as worms, brittle stars, and small crustaceans, often moving more actively over the bottom than heavier-bodied flatfish. Their elongated pectoral fins may aid in stabilization or subtle movement while resting on the seafloor. The species undertakes seasonal depth migrations related to feeding and spawning, generally moving to deeper water during colder months. Spawning produces pelagic eggs and larvae that drift in the water column before settling to the bottom and completing metamorphosis into the flattened juvenile form, after which they take up a deeper-water demersal existence.