The Gilded Triggerfish (Xanthichthys auromarginatus) is also known as the Blue Cheeked Triggerfish, the Blue Jaw Triggerfish and the Blue Throat Triggerfish. Triggerfish obtain their name from the locking mechanism used to hold the dorsal spine in place. The main dorsal spine is kept erect by a second spine which locks the dorsal spine in place.
Only when this trigger spine is moved can the main spine be lowered. The spine is used for defensive purposes because when raised it makes it difficult for a larger predator to swallow them. The spine is also used to lock the fish into crevices or small spaces making it difficult for predators to extract them. Triggerfish are adept at sliding into small thin crevices and their dorsal spines are then erected to lock them into place. Triggerfish swim by undulating their dorsal and anal fins.
The Gilded Triggerfish has an oval laterally compressed body, with its eyes set high on the body and far back from the mouth. This protects the eyes when dealing spiny prey. Their skin is thick and leather like with non over lapping scales. They have a small slightly upturned mouth ringed in dark blue.
The body is an overall blue grey colour with a thin brown line across the dorsal area. The eyes are brown and slightly bulging with a pale blue stripe around them and there is a single white mark ahead of the eye. From behind the gills lines of white dots formed by the scales run across to the caudal area. In males pictured above, there is a blue patch on the cheek and the edge of the dorsal, anal and caudal fins are lined in yellow. The females pictured below have a light brown edging to the dorsal, anal and caudal fins. Adults can grow up to 30 cm in length although they are usually closer to 20 cm in Tanzanian waters.
GILDED TRIGGERFISH IN THE WILD
In Tanzanian coastal waters they are fairly rare but on some remote offshore reefs they are common. They seem to prefer deeper off shore reefs with lots of current on the top of walls or on shelving drop offs from around 23 meters downwards to 35 meters. On these reefs there are loose aggregations of several hundred fish all swimming just above the bottom and then darting upwards into the water table to feed.
When a diver approaches they quickly slip into holes in the reef. Sometimes a male and female will go into the same hole. On some of the offshore reefs we found them on, there were many more males than females but this just from single dives on the reefs.
Gilded Triggerfish are found across the Indo west Pacific area from South Africa to Southern Japan, and the southern Great Barrier Reef and across to Hawaii.
Gilded Triggerfish have a relatively small up turned mouth designed to feed on plankton. Their favorite prey is reported to be copepods, small crustaceans which are free swimming. That said we also observed them occasionally picking food of the substrate although it was not possible to see what they picked on.
Breeding with Triggerfish takes place between one male and a single female. The females lay their eggs on the substrate and they are fertilized by the male. The eggs are then guarded by the female to prevent them from being eaten by predators. While the female is guarding the eggs their behavior can be very aggressive.
Gilded Triggerfish are kept by some aquarists. They tend to be kept in fish only tanks but if well fed some specimens may not take ornamental shrimp and hermit crabs and some people consider them reef safe. They require a large tank because of their potential size and are well known for jumping out of tanks. Clean water is a prerequisite for these fish.
Triggerfish are supposedly very good eating and are targeted by fishermen in some areas. They are caught in some areas by fishermen who drive them into nets.