Fringed Flounder, Etropus crossotus
Fringed Flounder, Etropus crossotus. Fish caught with a cast net off a pier in Puerto Adolfo Lopez Mateos, Baja California Sur, May 2018. Length: 14 cm (5.5 inches). Identification courtesy of H.J. Walker, Jr., Scripps Institution of Oceanography, La Jolla, California.
Fringed Flounder, Etropus crossotus. Fish provided by the commercial fishermen of the greater Los Cabos area, Baja California Sur, July 2009. Length: 21 cm (8.3 inches).
Fringed Flounder, Etropus crossotus. Fish caught from coastal tidal pools on Los Conchas Beach, Puerto Peñasco, Sonora, November 2022. Length: 21 cm (8.3 inches). Catch, photograph and identification courtesy of Luke Ovgard, Klamath Falls, Oregon.
The Fringed Flounder, Etropus crossotus, is a member of the Sand Flounder or Paralichthyidae Family, and is known in Mexico as lenguado ribete. Globally there are nine members of the genus Etropus, of which five are found in Mexican waters, two in the Atlantic, two in the Pacific, and this species in both the Atlantic and the Pacific Oceans.
The Fringed Flounder is a flatfish that has an elongated oval deep body with a depth that is 52% to 56% of standard length. Their eye side has a pale uniform brown appearance with narrow black scale margins. Their blind side is off-white to tan with some males having black pigmentation on their rear half. They have a short pointed head and a short very small mouth that does not reach the front edge of their large eyes. Their eyes are on the left side and set very close together with the lower eye slightly in front of the top eye. Their anal fin has 59 to 70 rays; their caudal fin has a blunt angular point; their dorsal fin has 75 to 89 rays; their pectoral fin is 50 to 75% of head length; and, their pelvic fins originate mid-body. They have 6 to 10 gill rakers on their lower arch. They are covered with small rough scales. Their lateral line is relatively straight and starts at the top corner of their gill cover.
The Fringed Flounder is a demersal species that are found over and within sandy and muddy bottoms at depths up to 108 m (355 feet). They are known to enter brackish and marine waters. They reach a maximum of 22.0 cm (8.7 inches) in length. They are optimistic and well-camouflaged ambush predators that lie in wait half submerged on the ocean floor. The Fringed Flounder is poorly studied with very limited information available about their lifestyle and behavioral patterns including specific details on age, growth, longevity, movement patterns, diet, habitat use, and reproduction.
The Fringed Flounder is a resident of all Mexican waters of the Atlantic (including the Gulf of Mexico and the Caribbean) and the Pacific Oceans with the exception that they are absent from Guerrero Negro, Baja California northward along the central and northwest coasts of Baja.
The Fringed Flounder can be confused with the Intermediate Flounder, Etropus ciadi (large mouth) and the Peruvian Flounder, Etropus peruvianus (body depth less than 50% of standard length).
From a conservation perspective the Fringed Flounder is currently considered to be of Least Concern with stable, widely distributed populations. They are fairly common in some locations and caught as a by-catch by beach seines and shrimp trawlers they are too small in stature to be of interest to most.