Note: If this text file is the only page you can see in your browser, then please click HERE to load the full graphics enhanced version of the Triggerfish Information Centre.
The fishes of the order Tetraodontiformes are a diverse group of primarily marine fishes which are found around the world. They belong to the class Actinopterygii (ray-finned fishes) and are represented today by over 340 species which are placed in 10 families. Additional fossil taxa are known from as early as the the late Cretaceous period (90-95 million years ago), and many modern families are known from at least the Eocene period (55 million years ago). This clade contains four main subclades: the plectocretacicoids, triacanthoids, balistoids and tetraodontoids. Plectrocretacicoids are known only from fossils and are the sister group to all living tetraodontiforms. Triacanthoids contain the deep water spikefishes (Triacanthodidae) and the shallow water triplespines (Triacanthidae) of the Indo-Pacific. Balistoids contain the boxfishes (Aracanidae and Ostraciidae), the triggerfishes (Balistidae) and the filefishes (Monacanthidae). Finally, tetraodontoids contain the pursefishes (Triodontidae), the puffers (Tetraodontidae), the porcupinefishes (Diodontidae) and the molas or ocean sunfishes (Molidae).
Balistidae is derived from the Latin root balista, meaning a catapult. This is probably a reference to the "thorn like" dorsal spine and the ability of the fish to quickly retract and extend it. The epithet "catapult thorn" seems quite fitting for the triggerfish. Balistidae, the family distinction, is number 440 in Nelson's 1984 "Systematic list of the families of the fishes in the world". There are some 30 to 40 species of triggerfishes belonging to the Balistidae family, a snapshot of the current species list can be seen here. Triggerfishes were first described and catalogued in 1758, the most recent addition to the list coming in 1989. Triggerfishes are distributed widely throughout tropical waters, and a map illustrating this distribution can be seen here.
Triggerfishes are small to medium-sized marine fishes growing to somewhere between 5 and 25 inches (15 - 65 cm) in length when mature. They have deep, laterally compressed bodies with rough, rhomboid-shaped scales, often having small spines, which form a tough covering. They are back-boned fish, with 18 vertebrae. The forehead is high, the eyes being placed above a longish pointed snout which ends in a small mouth containing short, strong jaws. The eyeballs are capable of being rotated independently. The teeth are reduced to an outer series of eight in each jaw. In addition the non-protrusible upper jaw contains a second inner series of six plate-like teeth. The gill opening is reduced to small slit, often covered with a hard bony plate. A diagram of the basic triggerfish body shape and characteristics can be seen here - (Diagram). Most triggerfishes are colourful and are marked with patterns of lines and spots. In some triggerfish species, movements of the pelvic bones and the muscles which support the swim bladder can cause the bladder to vibrate, producing a drum-like sound.
The first dorsal fin is spiny and is restricted to no more than three spines. The first spine on the dorsal fin is very large and, when erected, the small second spine locks it into place. This spine acts as a trigger - hence the name triggerfish - which must be released before the spine can be depressed. The ability to lock the first dorsal fin in an upright position, provides a defense against being swallowed or dragged from crevices by predators. A diagram of the locking mechanism for the first dorsal fin can be seen here - (Diagram). The soft dorsal and anal fins are approximately equal and opposite and the caudal fin is either round, truncate, or lunate in shape, with 12 principal rays. The pectoral fins are small and the pelvic fins have been reduced to a small, movable spine which is placed at the end of a long pelvic bone.
Triggerfish all share a characteristic swimming action, known as "balistiform". The second dorsal fin and the anal fin are the chief means of propulsion. The fish glides forward by initiating movement across the fins from front to rear; opposing fins often move simultaneously. Both fins act rather like propellors, each being one blade of the propellor. The pectoral fins are used to control altitude, and the caudal fin provides lateral guidance. Triggerfishes rarely use beats of the tail (the typical fish pattern) unless they are engaging in short hurried flight when an extra burst of speed is required.
A short, and it has to
be said, not particularly clear, Quicktime Movie file of a pair of captive
Odonus Niger (Red Toothed Trigger) can be seen by clicking on the
camera. It's here if you really want it, but the file is just over
1 meg and may take some time to load. The fish don't look to be in very good
condition either. For a better idea, get yourself down to the local marine
fish suppliers, or visit your nearest decent sized marine aquarium.
Triggerfishes are bottom dwellers and usually live in seaward areas of coral reefs. Most triggerfishes are solitary diurnal carnivores. Many of the more colourful species live a peaceful life and spend their days nibbling on a wide variety of bottom animals including crabs, echinoderms, corals, worms and other fishes. Although larger triggers can become semi-tame, feeding from the hand, they have powerful jaws and separate very sharp teeth which are used to crush the corals, crustacea and molluscs which form the basic diet. At night, they hide away in crevices where they wedge themselves in place by resting on their pelvic spine and erecting and locking their dorsal spine.
Triggerfish usually lay demersal eggs on soft coral bed or in large circular nests dug in the sand. Some species defend these nests fiercely, and when guarding eggs will attack whatever enters their territory, including man. This behavior is only temporary and once the eggs have hatched the triggerfish will return to its friendly state. Other species abandon their eggs and let them hatch on their own, hoping that a good proportion of the hatched eggs will survive.
These fish do well with a lot of free swimming space and plenty of places in which to hide. Their natural habitat for the most part is on or around coral reef beds, and triggerfishes are comfortable in aquaria decorated with a mixture of rocks and sterilised coral skeletons. Older and larger specimens have their own ideas on aquarium decor, and will happily spend hours rearranging the tank whatever your personal wishes might be! Generally peaceful when small, triggerfishes will sometimes display aggression towards their own kind, and to similarly sized and coloured fish of other species. A water temperature of around 26 degrees centigrade suits them well, and the salt content should be adjusted to a specific gravity of about 1.022
We've found them to be quite hardy in the home aquarium and they generally mix well with other fish, but avoid populating the tank with shrimps, crabs and snails as these form the basic triggerfish diet and will be readily consumed! Contrary to some opinions, triggerfishes do eat well in captivity, and will take shrimp (especially brine shrimp), squid, cockles, crabs, dried seaweed, fingers (if you're not fast enough), your mother-in-law, and face it, just about anything you put in front of them including air-lines and power cables!
Triggerfishes make excellent pets. They are inquisitive and friendly and will happily spend time watching you watching them. They have enormous personality and adapt well to life in a properly maintained marine aquarium. Be aware that several species of triggerfish will outgrow most home aquaria and care must be taken when selecting a suitable fish. Our experience is that an aquarium life of about five to six years can be expected, hopefully we can extend this as our skills improve.