Gymnothorax unicolor is a species belonging to the order Anguilliformes and family Muraenidae that together with 138 other species makes up the genus Gymnothorax. This species of Anguilliformes inhabits the waters of the eastern Atlantic Ocean as well as the Mediterranean Sea. It is found mainly on rocky bottoms from shallow water to 50 meters depth, with sporadic records of specimens up to 300 meters.
The body of Gymnothorax unicolor is typical of an eel, that is to say robust, elongated (up to 100 cm) and slightly flattened laterally. In fact, the height of the body is slightly higher than that of other moray eels. The head and snout are short and there are two openings that do not have a tube as in other species. The eyes are relatively small for the size of the head and are located approximately half the length of the jaw. The mouth has numerous sharp teeth forming three stripes (two lateral and one central). The dorsal fin starts almost at the level of the head, just behind the gill opening, which in this species is a small horseshoe-shaped opening, that is usually dark in color. The dorsal fin runs the entire length of the individual, and merges at the tail with the anal fin. They do not have pectoral fins or ventral fins.
As for the coloration of Gymnothorax unicolor, the color is usually brown or dark reddish, the front of the body being slightly darker than the rear. Both the dorsal and anal fins have yellowish margins.
Gymnothorax unicolor specimens are solitary, and spend the day hiding in cracks and crevices of rocks. During the night, they come out of their hiding places to look for their prey, mainly crustaceans, cephalopods and gastropods, which they detect thanks to their developed olfactory capacity.
Although the reproduction of this species is not extremely well studied, it is known that the juveniles of this species are hermaphrodites, and that depending on the environmental conditions in which they grow, they eventually develop one sex or the other.
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