The Redtoothed Triggerfish (Odonus niger) is also known as the Blue Triggerfish, Redfang Triggerfish and Niger 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 Redtoothed Triggerfish has an oval laterally compressed body, with its eyes set high on the body and far back from the mouth.Their skin is thick and leather like with non over lapping scales. They have a relatively small upturned mouth with protruding teeth and some specimens have red teeth. Their teeth continue growing with age and are constantly worn down in their natural habitat.
The tail is crescent shaped and the lobes elongate considerably with age. The pectoral fin is small and the anal and dorsal fins are large and elongated. These two fins are used for propulsion and are constantly undulating giving them an unusual looking swimming style.
The body is an overall dark blue colour with a light greenish blue colour between the scales on the body which are non overlapping. This creates a cross hatched pattern. The facial area is a light blue green colour below the mouth and there are a series of horizontal blue lines running across it. Two oblique blue lines run from the eye to the mouth.
Adults can grow up to 50 cm in length although they are usually between 30 cm and 35 cm in Tanzanian waters.
REDTOOTHED TRIGGERFISH IN THE WILD
In Tanzanian coastal waters they are common on seaward reefs with deep drop offs and slopes with lots of current. They seem to prefer depths of 15 to 30 meters and form large shoals, all swimming above or off the substrate. Juveniles are found on features in rubble areas and we have also seen them on protected reefs at depths of 12 to 15 meters. When a diver approaches too close they quickly slip into holes in the reef often with the tail protruding as can be seen below. If a pair is nesting they may attempt to warn a diver off the area
Redtoothed Triggerfish are found across the Indo west Pacific area from South Africa up to the Red Sea, across to Southern Japan, and down to the Great Barrier Reef and across to the Marquesas and Society islands.
Redtoothed Triggerfish have a relatively small mouth designed to feed on zooplankton and sponges.
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 they are guarding the eggs their behavior can be very aggressive. Male Redtoothed Triggerfish are territorial and maintain harems of up to ten females. Once the eggs hatch they have a long larval stage but little is known of this stage of their lives.
Redtoothed 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 all supposedly very good eating and are targeted by fishermen in some areas. Redtoothed Triggerfish are caught in some areas by fishermen who drive them into nets.