Black Durgon, Melichthys niger
The Black Durgon, Melichthys niger, whose common Spanish name is cochito negro, is a species in the Triggerfish or Balistidae Family, known collectively as cochitos in Mexico. This fish is also known as the Indian Triggerfish and the Black-finned Triggerfish. Globally, there are only three species in the genus Melichthys, of which one is found in Mexican waters of the Atlantic and the Pacific.
The Black Durgons have elongated, oval, robust, and compressed bodies with a depth that is 40% to 43% of standard length. They are very colorful having a pale blue base color covered with black diamond spots forming inconsistent dark lines throughout their body. They have black wavy lines radiating dorsally and anteriorly from their eyes. They have a pale blue-white line along the base of their anal and dorsal fins. All their fins are black. Their head has a wide yellow bar than runs from the beak to the center of the eyes. They are capable of changing colors to match their surroundings. They have small eyes and a small mouth that opens just above the center line and is equipped with heavy outer teeth on the upper and lower jaws. They have a small gill slit on their sides before the pectoral fin base. Their anal fin has 28 to 32 rays with the anterior rays being elevated. Their caudal fin is strongly concave. Their dorsal fin has three spines, the first which can be locked erect and the second which measures about half the length of the first, and 30 to 35 rays with the anterior rays being elevated. They have 8 to 10 lateral ridges on the rear of their body and caudal base. Their pelvic fins and lateral lines are inconspicuous. They are covered with thick scales.
The Black Durgons are a benthopelagic species found on the slopes of oceanic reefs and around oceanic islands at depths up to 250 feet. They reach a maximum length of 51 cm (20 inches). They are found in small loose aggregations of up to 200 individuals. They are omnivores that feed on small fish, algae, phytoplankton, shrimp, squid, and zooplankton. Reproduction is oviparous and not well studied and documented. They have a lifespan of up to six years.
The Black Durgons have a very wide global distribution which is attributed to their long pelagic stage. In Mexican waters, they are found in all oceanic waters but with only limited documented populations in widespread and generally remote areas. In the Gulf of Mexico, they are considered uncommon but are found in Veracruz along the Yucatan Peninsula. In the Pacific, they have been found in numerous widely spaced specific locations and are abundant around the Clipperton Islands.
The Black Durgon is easy to identify within its range and cannot be confused with any other species. However, the Indian or Black-finned Triggerfish, Melichthys indicus from the Indian Ocean can be easily mistaken for a Black Durgon in the aquarium trade.
The Black Durgons are sold commercially and marketed fresh on a limited basis. They are used extensively by the aquarium trade due to their beauty and ease of care although they can be aggressive. From a conservation perspective, they are currently considered of Least Concern, being common and abundant in parts of their wide global distribution.
Black Durgon, Melichthys niger. Underwater photo taken in coastal waters off Kailua-Kona, HI, February, 2015. Length: 46 cm (18 inches). Photo courtesy of Bob Hillis, Ivins, UT.