![Balistapus undulatus](https://upload.wikimedia.org/wikipedia/commons/f/f1/Balistapus_undulatus.jpg)
The orange-lined triggerfish (''Balistapus undulatus'') is a
demersal
The demersal zone is the part of the sea or ocean (or deep lake) consisting of the part of the water column near to (and significantly affected by) the seabed and the benthos. The demersal zone is just above the benthic zone and forms a layer of ...
triggerfish
Triggerfish are about 40 species of often brightly colored fish of the family Balistidae. Often marked by lines and spots, they inhabit tropical and subtropical oceans throughout the world, with the greatest species richness in the Indo-Pacifi ...
. Although ''Balistapus'' is a
monotypic genus
In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...
, it is closely related to the genus ''
Balistoides''.
Description
The orange-lined triggerfish has a dark brown to dark green body with orange lines that start behind the head and cover the rest of its body.
Their maximum body size is about 30 centimeters.
Its body has a stocky appearance, oval shape, and is compressed laterally.
The head is large and is about one third of the body length.
The mouth is small and terminal and it has strong teeth.
The first
dorsal fin
A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through conv ...
has three spines, one of which is longer and stronger than the other.
It is erectile and kept in a dorsal furrow at rest.
The second
dorsal fin
A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through conv ...
is similar in shape and size to the
anal fin
Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...
, which is symmetrically opposed to it.
The
pelvic fin
Pelvic fins or ventral fins are paired fins located on the ventral surface of fish. The paired pelvic fins are homologous to the hindlimbs of tetrapods.
Structure and function Structure
In actinopterygians, the pelvic fin consists of two en ...
is reduced to a ventral protrusion.
[ They also typically have a large block spot by their peduncular spines, and the caudal fin is orange.]
In general, males tend to be larger and lack a concave snout, and also lose the lines on his snout as he matures. Females and juveniles are smaller and have a concave snout.
Distribution and habitat
While other balistoid fishes, such as the filefish and leatherjacks, are typically found all across the Indo-western Pacific, the triggerfish are typically found in coral reefs ecosystems, coral lagoons, and external reef slopes within this area, as well off the coast of east Africa, the Red Sea, and Japan. They tend to stay around their burrows and dens within the reef. Within coral reefs, the orange-lined triggerfish are more versatile than other triggerfish species and can be found at depths up to 50 meters, although studies have found that they prefer depths of 2 to 8 meters. No relationship between the area of the reef and depth has been found in juveniles, and adults were found to vary their depth based on the region; in general, the species was found to have a broad distribution across the reef. There is also a difference between the types of substrata that the adults and juvenile orange-lined triggerfish prefer: the adults were found to prefer rock and branching coral, while the juvenile fish were found to prefer softer surfaces.
Ecological role and feeding
The orange-lined triggerfish is an omnivorous feeder that can, because of its strong and heavy teeth, tackle a variety of benthic prey. Observed food items include cnidarians
Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter.
Their distinguishing feature is cnidocytes, specialized cells that th ...
, molluscs
Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant taxon, extant species of molluscs are recognized. The number of fossil sp ...
, ctenophores
Ctenophora (; ctenophore ; ) comprise a phylum of marine invertebrates, commonly known as comb jellies, that inhabit sea waters worldwide. They are notable for the groups of cilia they use for swimming (commonly referred to as "combs"), a ...
, crustaceans
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...
, other fish, algae
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
, and echinoderms
An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the sea li ...
. This species in particular, given its broad diet and distribution, is a crucial component in coral reef ecosystems through top-down control and especially through consumption of sea-urchins. The orange-lined triggerfish is a main and dominant predator of the burrowing urchin (''Echinometra mathaei
''Echinometra mathaei'', the burrowing urchin, is a species of sea urchin in the family Echinometridae. It occurs in shallow waters in the Indo-Pacific region. The type locality is Mauritius.
Description
''Echinometra mathaei'' grows to a ...
'') in East African marine parks. Before being protected, the population was overfished, which allowed the burrowing sea urchin population to grow rapidly. In these ecosystems, the burrowing sea urchin affects coral reef health, the presence of other grazers and algae, and erosion. With all three of these influences intertwined, the burrowing sea urchin has the ability to degrade coral reef ecosystems if they are not being controlled by predators, such as the orange-lined triggerfish. When compared to other predators of the burrowing sea urchin in the East African marine parks, the orange-lined triggerfish was found to consume more burrowing sea urchins than others, which exemplifies this species’ influence on coral reef ecosystems.
Behaviour
This triggerfish is diurnal, solitary, and territorial
A territory is an area of land, sea, or space, particularly belonging or connected to a country, person, or animal.
In international politics, a territory is usually either the total area from which a state may extract power resources or a ...
. It can be aggressive with other fish. It erects its first dorsal spine to intimidate opponents and predator
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...
s.
References
External links
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{{Taxonbar, from=Q1139189
Balistidae
Fish of Palau
Fish described in 1797