English name: Rex Sole (Threadfin Sole)

Scientific name:  Errex zachirus

Origin: Alaska, USA

Overview

Rex sole — also known as threadfin sole — is a right-eyed flatfish in the family Pleuronectidae. It is a demersal species native to the temperate waters of the North Pacific, 

prized for its delicate, mild-flavored flesh.

Distribution & Habitat

Rex sole occurs across the North Pacific, ranging from Baja California, Mexico, along the U.S. and Canadian coasts through Alaska, 

across the Bering Sea to the Russian coast and the Sea of Japan. It is a demersal fish found over sand or mud bottoms, most commonly at depths of 61–500 m (200–1,640 ft), 

though it has been recorded as deep as 1,100 m (3,600 ft).

Physical Description

Rex sole is a slow-growing, right-eyed flounder with an elongate, oval body and a small mouth. Adults typically reach about 36 cm (14 in) in length, 

with a maximum recorded length of 60 cm (24 in) and weight of 2.0 kg (4.4 lb). The maximum reported lifespan is 24 years.

Key identifying features include:

- Uniform light brown to grey coloration on the eyed (upper) side, covered in small scales

- Off-white blind (lower) side

- Dark dorsal and anal fins on the eyed side

- A long, mostly black pectoral fin on the eyed side (the "threadfin" feature)

- Rounded caudal fin

- Nearly straight lateral line

Diet

Rex sole feeds on benthic invertebrates, including crustaceans, worms, shrimp and crabs.

Commercial Importance

Rex sole is commercially harvested by trawler and forms a significant part of the Pacific flatfish trawl fishery, from California northward to the Bering Sea. 

Its flesh is delicate and mild in flavor, making it a versatile and valued table fish.