Larval rearing of the crosshatch triggerfish, Xanthichthys mento

January 01, 2014

Family: Balistidae > Genus: Xanthichthys > Species: X. mento

Triggerfishes are carnivorous, moderate sized (8 and 20 in) fishes, distinctive by their stout dorsal spine, oval shape, long snout, and small mouth with sharp teeth. The family comprises 40 species in 11 genera. Triggerfishes occur in subtropical and tropical seas worldwide and generally inhabit reefs, where they live singly, as pairs, in small groups or in schools and feed on benthic invertebrates, small fish and sometimes algae.  Many species play an important ecological role in controlling sea urchins and other benthic invertebrate populations and some are valuable and delicious food fish (queen triggerfish, grey triggerfish). Numerous triggerfish species also make hardy, bold and beautiful aquarium fishes though their aggressive tendencies can be downside. Triggerfishes are not farmed because of their long and complicated larval phase. Experimental captive-breeding has previously only been accomplished for the queen triggerfish.

The crosshatch triggerfish (Xanthichthys mento) is a rare, colorful, hardy and relatively timid triggerfish species that commands a high price in the aquarium trade. It occurs in the subtropical Pacific, including the Hawaiiian islands. A pair of crosshatch triggerfish were conditioned at the RCT hatchery for two month before they spawned. The pair reproduced approximately every 19-23 days and scattered up to a million eggs onto the tank bottom. Spawning took place in the morning and the eggs hatched the following evening.  The eggs are small (0.48 mm in diameter), spherical, adhesive and contain multiple oil droplets. First feeding larvae are moderate bodied, just 2.1 mm TL and have a very small mouth.

Features of triggerfish larvae include the very small mouth at first feeding, the raised cluster of spinules on the preopercle, the curved barbs on the first dorsal spine, the pelvic filament, the ovoid to round body shape and the extended pelagic juvenile stage. The larvae were raised on cultured ciliates (Strombidium sp.) followed by a combination of size strained cultured and wild copepods. The larval phase of X. mento is about 200 days. The small mouth size during the early larval stages, aggression during the later larval stages and the long pelagic larval and juvenile period makes this species unsuitable for aquaculture. This is the first documented rearing of a Xanthichthys species.