C-O Sole, Pleuronichthys coenosus

C-O Sole, Pleuronichthys coenosus. Fish provided by the commercial fishermen of the greater San Diego area, October 2014. Length: 32 cm (13 inches). Identification courtesy of H.J. Walker, Jr., Scripps Institution of Oceanography, La Jolla, California.

The C-O Sole, Pleuronichthys coenosus, is a member of the Righteye Flounder or Pleuronectidae Family, and is known in Mexico as platija de fango. Globally, there are eight species in the genus Pleuronichthys, of which five are found in Mexican waters, all in the Pacific Ocean.

The C-O Sole has an oval fusiform highly compressed body that is widest in the middle with a depth that is 52% to 56% of standard length. They vary in color from off-white to very dark brown and almost black (the most common) and have significant mottling. Their blind side is off-white. Their head has relatively large protruding eyes on the right side that are significantly elevated. There is a prominent ridge between their eyes and the top eye precedes the lower eye slightly. They have a small asymmetrical mouth with thick lips. They have a characteristic dark spot in the center of their caudal fin rays and a crescent mark where the caudal fin rays meet the body giving a “C-O” pattern, after which they are named. These markings are difficult to see in some fish including the fish pictured above. They also have a dark spot about the size of the eyes located mid-body on their lateral line. Their anal fin is high on the body and has no spines and 46 to 56 rays; their caudal fin is deep and rounded; their dorsal fin is high on the body and has no spines and 65 to 78 rays; and, their pectoral fins are moderately long and bluntly pointed. They have a straight lateral line that originates above their eyes.

The C-O Sole is a demersal species that is found over and within sandy and muddy bottoms that are adjacent to hard structures (such as reefs and breakwaters) normally at depths less than 30 m (100 feet) but occasionally also at depths up to 350 m (1,145 feet). They reach a maximum of 36 cm (14 inches) in length and 450 g (1 lb) in weight. They are opportunistic well-camouflaged ambush predators that lie in wait half-submerged on the ocean floor consuming crustaceans (brittle stars, clams, crabs, polychaetes, and shrimp) and small fish. In turn they are preyed upon by Common Bottlenose Dolphin, Tursiops truncatus, and  Copper Rockfish, Sebastes caurinus. The C-O Sole 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 C-O Sole is a resident of Mexican waters of the Pacific Ocean but has a limited distribution being found from Guerrero Negro, Baja California, northward along the central and northwest coasts of Baja.

The C-O Sole is not easily confused with any other fish due to its markings, protruding eyes, and uniquely shaped tail.

From a conservation perspective the C-O Sole has not been formally evaluated. They are small in stature and difficult to catch by hook due to their very small mouth. Hooks of size 4 or less baited with bloodworms, lugworms, and ghost shrimps work best. They are taken infrequently on party boats, occasionally off piers adjacent to deep water, and rarely from shore. They are deemed a high quality food fish although relatively small in stature and difficult to fillet. They can be found for sale on rare occasions at dockside markets in California.