News / Species Spotlight / Lunula Triggerfish (Rhinecanthus lunula) (07/17/18)

Lunula Triggerfish (Rhinecanthus lunula)

Species Spotlight - Lunula Triggerfish (Rhinecanthus lunula)
Like the Conspicuous Angelfish (Chaetodontoplus conspicillatus) and the Femininus Wrasse (Anampses femininus), the legendary Lunula Triggerfish is found only in the South Pacific, making it quite the rarity within the aquarium trade. And compounding this rarity is its preference for deeper reefs (10-30 meters) around oceanic islands, which helps to make this one of the holy grails among the family Balistidae.

Rhinecanthus is the largest genus of triggerfish, despite having just seven species in total. Here we find such familiar fare as the Picasso Triggerfish (R. aculeatus) and Wedge-tail Triggerfish (R. rectangularis). A bit less commonly, theres the closely related Blackbelly Triggerfish (R. verrucosus) and its Arabian cousin, the Assasi Triggerfish (R. assasi).

The remaining three species are each exceedingly uncommon and share an elongated body shape, a black band circling the caudal peduncle, and a yellow caudal fin. The rarest of the lot is the Deepwater Triggerfish (R. abyssus), known from just FOUR SPECIMENS collected at great depth in the Ryukyu Islands and Sulawesi. It stands out for the absence of the half-moon shaped line at the back half of the fish. In the Indian Ocean, the Mauritian Triggerfish (R. cinereus) lacks any yellow markings on its face, has a mostly dark bar beneath its eye, and has noticeably more yellow along its sides. It occurs sporadically in aquarium exports from Mauritius, with additional reports of this species from Reunion and the Maldives, though it no doubt occurs more widely in the region.

And then theres the South Pacifics balistid jewel, R. lunula, which is well-known from Eastern Australia to Pitcairn. The species is named for the characteristic arcing line in its rear portions, which resembles a crescent moon (lunula translates from Latin as little moon). This is, of course, something which is shared with its Indian Ocean cousin, and, interestingly, that species was scientifically described almost two-hundred years prior to the recognition of R. lunula in 1983, first appearing in the now defunct magazine Freshwater and Marine Aquarium.

The difference between it and R. cinereus relates to the cheery yellow line that partially encircles the mouth and another (shared with R. abyssus) that stretches from the mouth to the pectoral fin. The dark eye bar of R. cinereus is here an attractive mix of blue and black stripes, while the back half of the fish is largely tan or grey, absent the yellow swath seen in its sister species. Its arguable which of these three is the most beautiful, though certainly R. lunula is the most attainable for aquarists, albeit at a considerable price.

Like most triggerfishes, the Lunula is a hearty beast once acclimated to aquarium life. Newly imported specimens can sometimes be a bit underweight after their travels, which is most easily observed by a sunken in shape to the head and back. Heavy feedings of meaty foods (silversides, krill, etc), along with a prophylactic dose of praziquantel to control any internal worms is a good course of action. The species is robust and semi-aggressive, but, generally, not too obnoxious to tankmates.