News / Species Spotlight / Goldenback Triggerfish (Xanthichthys caeruleolineatus) (07/10/18)

Goldenback Triggerfish (Xanthichthys caeruleolineatus)

Species Spotlight - Goldenback Triggerfish Xanthichthys caeruleolineatus
Xanthichthys triggerfishes are the cream of the balistid crop, but few aquarists have had the pleasure of keeping the elusive species in todays spotlight. The Goldenback Triggerfish (X. caeruleolineatus) is the largest member of this small group (by about two inches), but its the tall body profile that really stands out compared to its more elongated cousins.

Youll find the Goldenback across a vast swath of the Indo-Pacific, though documented instances of it are surprisingly few and far between for such a large and easily recognized species. In the Indian Ocean, it occurs from South Africa to Christmas Island and the Maldives. In the Pacific, its been found at Okinawa, in the Coral Sea, French Polynesia, Micronesia. It was found for the first time in Hawaii as recently as 1993, which is remarkable given how well-studied that archipelago is. And you can even see this fish in the Galapagos Islands and Cocos Island off Costa Rica. Oceanic islands are the common thread here, and its only at great depth that this fish becomes truly abundant. Though reports put it as shallow as 15 meters, this triggerfish really only frequents reefs below about 45 meters, and the range is stated to extend down to at least 200 meters! So it should be little surprise that specimens are hard to come by in the aquarium world.

But recent years have seen an uptick in the availability of the Goldenback. Specimens have been an uncommon export from places like Kiritimati and the Marshall Islands, but a large population located at Scarborough Shoal has just now started to be fished thanks to a relaxation of the hostilities between the Philippines and China in the South China Sea. Its nice to see the easement of political strife leading to some direct piscine gains.

Compared to others in its genus, X. caeruleolineatus stands out for the sharp contrast in color across its back, along with a sweeping blue line delimiting the golden back from the lightly colored belly. This is alluded to in the species name, which translates as blue-lined.

Interestingly, juveniles of this fish are markedly different in their morphology and coloration. When first settled out from the plankton, they are mostly black, with numerous white spots (a vestige of which remains present in adults during their stress/nocturnal coloration). Most unusually, the young have a large bulge beneath the pectoral fins that lead its discoverer to place it in a new genus, Xenobalistes. It was only when a specimen washed ashore in South Africa and was raised by ichthyologist Phil Haemstra into adulthood that its true nature was discovered.

In an aquarium, this species should be treated to ample swimming space. At more than a foot long as an adult, a tank of massive dimensions is recommended, along with heavy water movement and heavy filtration. Clean, well-oxygenated water is a hallmark of the deep oceanic habitats this fish comes from. Otherwise, its care is not all that different from others in its genus, which tend to be relatively mild-mannered compared to many triggerfishes.