Sargassum Triggerfish, Xanthichthys ringens
Sargassum Triggerfish, Xanthichthys ringens. Fish caught from within the Gulf of Mexico off Cocodrie, Louisana, April, 2017. Length: 20 cm (7.9 inches). Catch, photograph and identification courtesy of Dominick Porcelli, Lighthouse Point, Florida.
The Sargassum Triggerfish, Xanthichthys ringens, that is also known as the Red Tail Triggerfish and whose common name in Mexico is cocuyo, is a member of the Triggerfish or Balistidae Family. They are named for the behavior of the juveniles that are normally found in close proximity to floating Sargassum. Globally, there are three species in the genus Melichthys, of which one is found in Mexican waters of both the Atlantic and the Pacific Oceans.
The Sargassum Triggerfish has a slightly elongated rhomboid, robust and compressed body. They are an overall light brown color. Their body scales are set in rows along the sides and have dark pigment between them that affords rows of dark brown spots on the body. Their cheeks have three diagonal grooves that run from below and behind the mouth to the gill openings that are deep blue. The base of the anal and dorsal fins and membranes of the first dorsal fin are dark brown. The caudal fin has a large orange-red crescent and has an orange-red margin along the top, bottom and rear. The outer part of the eyes have a wide blue-white ring. They have a small mouth that opens above the center line of the body with a projecting lower jaw. They have 8 heavy outer teeth on both jaws. Their anal fin has 23 to 27 rays; their caudal fin is concave; their first dorsal fin has 3 spines with the second spine being greater than half the size of the first and the third is very small; their second dorsal fin has 26 to 30 rays; and their pelvic fins are very small. They are covered with thick leathery skin with large scales. Their lateral line is inconspicuous.
The Sargassum Triggerfish are normally found as solitary individuals or in small groups over deep covered with seaweed reefs at depths up to 190 m (625 feet) but seldom above 30 m (100 feet) and normally between 30 m (100 feet) and 60 m (200 feet). They reach a maximum of 25 cm (9.8 inches) in length. They are diurnally active omnivores that feed on small fish, algae, crabs, phytoplankton, sea urchins, shrimp, squid, and zooplankton. They are known to be highly destructive within the reefs ecosystem. They utilize their dorsal spines for defense which are also used to lock themselves in place while sleeping. Reproduction is oviparous and occurs in deep water with millions of eggs laid on the bottom and carried for by both parents. They do not use their caudal fin for locomotion. They can move each eye in all directions independent of the other. The Sargassum Triggerfish is poorly studied with very limited information available about their lifestyle and behavioral patterns including specific details on age, growth, longevity.
The Sargassum Triggerfish 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 Sargassum Triggerfish is similar in overall appearance to five Triggerfish found in Mexican waters of the Atlantic Ocean, the Black Durgon, Melichthys niger, the Gray Triggerfish, Balistes capriscus, the Ocean Triggerfish, Canthidermis sufflamen, the Queen Triggerfish, Balistes vetula, and the Rough Triggerfish, Canthidermis maculate, but is the only one that has a red tail.
From a conservation perspective, the Sargassum Triggerfish is currently considered to be of Least Concern with stable, widely distributed populations. They are used extensively by the aquarium trade due to their beauty and ease of care although they can be aggressive.