Sargassum triggerfish (Xanthichthys ringens)
Triggerfishes are members of the family Balistidae, sometimes considered one of the more evolutionarily advanced families of marine fish. A dozen genera comprise the family, which totals less than 40 species. Certain characteristics are shared by all members of the family, notably two dorsal fins but no pelvic fins, eight teeth on the front jaw followed immediately by an additional six teeth and a large, well-developed pharyngeal plate which is well-suited for crushing various hard-shelled crustaceans.
Four species are represented in Indo-Pacific waters, yet Xanthichthys ringens is known only from the Atlantic Ocean. Specimens have been collected from as far north as South Carolina and extending as far south as Brazil. St. Lucia, Florida and Cuba all have healthy populations. Perhaps the largest geographical distribution of the genus occurs in X. caeruleolineatus, which is present from the Tuamotu Archipelago to the St. Brandon's Shoals. Another distribution point worth mentioning is the anti-tropical distribution of X. mento and how both pre-juveniles of X. mento and X. ringens have been found up to 500 miles off the coast.
Like its Indo-Pacific brethren, X. ringens prefers deeper waters near steep dropoffs and is "rarely encountered at depths of less than 100 feet" (Randall, 1968). At least one submarine observation has noted X. ringens patrolling about 400 feet deep off the Jamaican coast. No specimens of X. caeruleolineatus have been collected using traditional SCUBA equipment, probably because most individuals have been found at depths of 600 feet or more.
A slightly upturned mouth, which remains very small throughout the fish's lifespan, does not allow Xanthichthys to consume the same foods as many other triggerfishes. Instead, species of the genus Xanthichthys concentrate their diet on free-floating zooplankton, which they eagerly pluck from the water column. In fact, stomach contents of X. auromarginatus revealed the fish fed exclusively on zooplankton (Hobson, 1974). Additional notes from this study indicated the vast majority of the zooplankton were calanoid copepods.
Two species are known to display distinct sexual dichromatism between the adult males and females. This led to some confusion about species classification, but that was nevertheless worked out more easily than in most other dichromatic genera. Xanthichthys auromarginatus and X. mento each have beautiful male colorations while the females are certainly less attractive and flashy
Date 30 December 2008, 12:00:53
Source originally posted to Flickr as Sargassum Triggerfish (Xanthichthys ringens)
Author Cliff http://flickr.com/photos/28567825@N03
Xanthichthys ringens, the Sargassum triggerfish, is a species of triggerfish from the Western Atlantic, ranging from North Carolina (USA) to Brazil. It occasionally makes its way into the aquarium trade. It grows to a size of 25 centimetres (9.8 in) in length. Order: Tetraodontiformes, Family: Balistidae.