Dusky Flounder, Syacium papillosum

Dusky Flounder, Syacium papillosum. Fish caught from coastal waters off Big Pine Key, Florida, April 2018. Length: 18 cm (7.1 inches). Catch, photograph and identification courtesy of Marc Eberlein, Grand Rapids, Michigan.

Dusky Flounder, Syacium papillosum. Fish caught from coastal waters off Sebastian, Florida, December 2022. Length: 20 cm (7.9 inches). Catch, photograph and identification courtesy of Ben Cantrell, Sebastian, Florida.

Dusky Flounder, Syacium papillosum. Fish caught in the Florida Middle Grounds, February 2019. Length: 25 cm (9.8 inches). Catch and photograph courtesy of George Brinkman, Guelph, Ontario, Canada.

The Dusky Flounder has an elongated oval-shaped bodies that have a depth that is 40% to 44% of standard length. Their eye side varies in color from a uniform gray-brown to a light tan with some fish having dark blotches. Their blind side is dusky. The pectoral fins have three or four dark bars. Their head has a medium-sized mouth that is equipped with two rows of teeth on the upper jaw and one row on the lower jaw and ends under the middle of their widely spaced eyes found on the left side with the lower eye occurring well before the upper eye. Their anal fin has 63 to 75 rays; their caudal fin has a wide base and is round; and, their dorsal fin has 79 to 94 rays. They are sexually dimorphic with females being larger than males and the males having extended first and second pectoral fin rays. They have 10 to 12 gill rakers. They are covered with smooth scales. Their lateral line is straight and does not extend into their head.The Dusky Flounder, Syacium papillosum, is a member of the Sand Flounder or Paralichtyidae Family, that is known in Mexico as lenguado moreno. Globally, there are eight members of the genus Syacium, of which six are found in Mexican waters, three in the Atlantic and three in the Pacific Ocean.

The Dusky Flounder is a demersal species that is found over and within sandy and muddy bottoms at depths between 4 m (15 feet) and 150 m (500 feet). They reach a maximum of 30.0 cm (11.8 inches) in length. They are opportunistic and well-camouflaged ambush predators that lie in wait half submerged on the ocean floor. They are adversely affected by hypoxia (low oxygen) and will move to deeper waters during such episodes. They prey on small fish and a wide variety of crustaceans including penaeid shrimp. Reproduction is oviparous with each female producing numerous eggs in multiple spawning’s over a prolonged spawning period. The Dusky 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 Dusky Flounder is a resident of all Mexican waters of the Atlantic Ocean including the Gulf of Mexico and the east coast of the Yucatán Peninsula in the Caribbean.

The Dusky Flounder is most likely confused with the Channel Flounder, Syacium micrurum (eyes close together, not off set), and the Shoal Flounder, Syacium gunteri (body depth 50% to 56%; uniform brown color without spotting).

From a conservation perspective the Dusky Flounder is currently considered to be of Least Concern with stable, well documented populations. Their long term viability is threatened by habitat destruction via deep waters trawlers. They are caught with some frequency as a by-catch in shrimp trawl fisheries and marketed fresh.