The Yellow Margin Triggerfish (Pseudobalistes flavimarginatus) is also known as the Yellowmargin Trigger,Yellowface Triggerfish and Pineapple 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.
The Yellow Margin Triggerfish has a typical Triggerfish shape, with its eyes set high on the body and far back from the mouth. This protects the eyes when dealing with prickly urchins and some crustaceans. The skin is thick and leather like, also for protection from spiny and spikey prey. The relatively small mouth with strong large teeth gives it a very powerful bite.
The adult has a series of diamond shaped whitish yellow markings across its body. The facial area and lower body is a yellowish colour and the main body is a yellowish brown color. Spread across the body are a series of black spots and these are concentrated around the eye. The eye is bulbous with a yellow ring around it with brown marks on it. The rear dorsal fin, anal and caudal fins have dark markings on them tipped with yellow giving the fish its common name.
The juvenile pictured below is far more colorful and has a yellow lower body with alternating dark blue and white blotches across the dorsal area. Overlaying these colours are irregular light blue lines running roughly horizontally across the body. The fins are a light blue colour.
Adults can grow up to 60 cm in length and the World Record for a line caught specimen is 5.61 kg. This specimen was 55.88 cm in length so a full grown specimen could weigh slightly more.
YELLOW MARGIN TRIGGERFISH IN THE WILD
The Yellow Margin Triggerfish is usually seen on protected reefs and rubble and sandy areas from 5 meters downwards. The areas they favor are often silty making it difficult to photograph them well. They are adept at sliding sideways into crevices as can be seen in the image below. Sometimes they go into a crevice that one does not notice and that seems impossible for them to fit in, yet they do. Usually they are seen solitary and research in Okinawa on similar species indicated that a male would have a territory overlapping that of three females.
CAUTION FOR DIVERS ON THE YELLOW MARGIN TRIGGERFISH
When the female is guarding eggs they may become slightly aggressive towards divers but not on the level of the Titan Triggerfish. When this occurs common sense dictates one should horizontally reverse away from them as they could deliver a painful bite. Usually once the female sees you are leaving they back off.
Yellow Margin Triggerfish are found across the Indo west Pacific area from South Africa to Southern Japan, and the southern Great Barrier Reef across into the Pacific Islands.
Titan Triggerfish have a varied diet and feed on gatropods, corals, tunicates, sea urchins and foraminiferans. Their large teeth and powerful mouth are used to crush their prey.
Breeding with the Yellow MarginTriggerfish takes place between one male and a single female. The females lay their eggs on the sand in a 2 meter wide depression that is 70 cm deep. The eggs are held in place by pieces of rubble. 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 aggressive.
Although the juveniles are very attractive looking fish, they are not commonly kept in aquariums because of their size and territorial behavior. Beyond any question of a doubt they are not reef safe and great care has to be taken with their tank mates as they will likely attack smaller fishes. They are really not suitable for home aquariums. Because of their sharp teeth and propensity to bite great care should be taken with these fish.
Yellow Margin Triggerfish are supposedly very good eating and are targeted by fishermen in some areas. They are caught in some areas by fishermen using a relatively small hook baited with a whole prawn or other crustacean and additionally will take lures or flies. This is unfortunate as they play a great role in keeping sea urchin populations in check.