Triggerfish are about 40 species of often brightly colored fish of the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Balistidae. Often marked by lines and spots, they inhabit

tropical The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred to ...

and subtropical oceans throughout the world, with the greatest

species richness Species richness is the number of different species represented in an ecological community, landscape or region. Species richness is simply a count of species, and it does not take into account the abundances of the species or their relative ab ...

in the Indo-Pacific. Most are found in relatively shallow, coastal habitats, especially at

coral reef A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups. C ...

s, but a few, such as the oceanic triggerfish (''Canthidermis maculata''), are

pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or w ...

. While several species from this family are popular in the marine aquarium trade, they are often notoriously ill-tempered.

Anatomy and appearance

The largest member of the family, the stone triggerfish (''Pseudobalistes naufragium'') reaches , but most species have a maximum length between . Triggerfish have an oval-shaped, highly compressed body. The head is large, terminating in a small but strong-jawed mouth with teeth adapted for crushing shells. The eyes are small, set far back from the mouth, at the top of the head. The anterior

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 c ...

is reduced to a set of three spines. The first spine is stout and by far the longest. All three are normally retracted into a groove. Characteristic of the order

Tetraodontiformes The Tetraodontiformes are an order of highly derived ray-finned fish, also called the Plectognathi. Sometimes these are classified as a suborder of the order Perciformes. The Tetraodontiformes are represented by 10 extant families and at least ...

, the anal and posterior dorsal fins are capable of undulating from side to side to provide slow movement and comprise their primary mode of

propulsion Propulsion is the generation of force by any combination of pushing or pulling to modify the translational motion of an object, which is typically a rigid body (or an articulated rigid body) but may also concern a fluid. The term is derived f ...

. The sickle-shaped

caudal 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 ...

is used only to escape predators. The two pelvic fins are overlaid by skin for most of their length and fused to form a single spine, terminated by very short rays, their only external evidence. Gill plates ( opercula), although present, are also not visible, overlaid by the tough skin, covered with rough, rhomboid

scales Scale or scales may refer to: Mathematics * Scale (descriptive set theory), an object defined on a set of points * Scale (ratio), the ratio of a linear dimension of a model to the corresponding dimension of the original * Scale factor, a number w ...

that form a stout armor on their bodies. The only gill opening is a vertical slit, directly above the

pectoral Pectoral may refer to: * The chest region and anything relating to it. * Pectoral cross, a cross worn on the chest * a decorative, usually jeweled version of a gorget * Pectoral (Ancient Egypt), a type of jewelry worn in ancient Egypt * Pectorali ...

fins. This peculiar covering of the gill plates is shared with other members of the Tetradontae. Each jaw contains a row of four teeth on either side, while the upper jaw contains an additional set of six plate-like

pharyngeal teeth Pharyngeal teeth are teeth in the pharyngeal arch of the throat of cyprinids, suckers, and a number of other fish species otherwise lacking teeth.predators, triggerfish can erect the first two dorsal spines: The first (anterior) spine is locked in place by erection of the short second spine, and can be unlocked only by depressing the second, “trigger” spine, hence the family name “triggerfish”. With the exception of a few species from the genus '' Xanthichthys'', the sexes of all species in this family are similar in appearance.

Behavior

The rather bizarre anatomy of the triggerfish reflects its typical diet of slow-moving, bottom dwelling crustaceans,

mollusk 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 species of molluscs are recognized. The number of fossil species is e ...

s, sea urchins and other

echinoderm 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 s ...

s, generally creatures with protective shells and spines. Many will also take small fishes and some, notably the members of the genus ''

Melichthys ''Melichthys'' is a small genus in the triggerfish family ( Balistidae). Member species are found in the Indian Ocean, Pacific Ocean and even the Red Sea (''M. niger''). The Black triggerfish is the largest species in this genus at 45 cm in ...

'', feed on algae. A few, for example the redtoothed triggerfish (''Odonus niger''), mainly feed on

plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a crucia ...

. They are known to exhibit a high level of intelligence for a fish, and have the ability to learn from previous experiences. Some triggerfish species can be quite aggressive when guarding their eggs. Both the picasso (''Rhinecanthus aculeatus'') and titan triggerfish (''Balistoides viridescens'') viciously defend their nests against intruders, including scuba divers and snorkelers. Their territory extends in a cone from the nest toward the surface, so swimming upwards can put a diver further into the fishes' territory; a horizontal swim away from the nest site is best when confronted by an angry triggerfish. Unlike the relatively small picasso triggerfish, the titan triggerfish poses a serious threat to inattentive divers due to its large size and powerful teeth.

Male territoriality

Triggerfish males migrate to their traditional spawning sites prior to mating and establish territories. Some male species (i.e.'' Balistes carolinensis'' and '' Pseudobalistes flavimarginatus'') build hollow nests within their territories. Triggerfish males are fierce in guarding their territories as having a territory is essential for reproduction. A male's territory is used for spawning and parental care. Most male territories are located over a sandy sea bottom or on a rocky reef. A single territory usually includes more than one female, and the male mates with all of the females residing in or visiting his territory (

polygyny Polygyny (; from Neoclassical Greek πολυγυνία (); ) is the most common and accepted form of polygamy around the world, entailing the marriage of a man with several women. Incidence Polygyny is more widespread in Africa than in any ...

). In Hachijojima, Izu Islands, Japan, one male crosshatch triggerfish ('' Xanthichthys mento'') has up to three females in his territory at the same time, and mates with them in pairs. Each male red-toothed triggerfish ('' Odonus niger'') mates with more than 10 females in his territory on the same day. Yellow margin triggerfish ('' Pseudobalistes flavimarginatus'') also exhibit polygyny.

Spawning and biparental care

Triggerfish spawning is timed in relation to lunar cycles, tides, and time of changeover of tides. In relation to lunar cycles, eggs are observed 2–6 days before the full moon and 3–5 days before the new moon. In relation to tides, spawning happens 1–5 days before the spring tide. In relation to timing of tides, eggs are observed on days when high tides take place around sunset.

Male and female triggerfish perform certain prespawning behaviors: blowing and touching. A male and female blow water on the sandy bottom (usually in the same spot at the same time) and set up their egg site. They touch their abdomens on the bottom as if they are spawning. During actual spawning, eggs are laid on the sandy sea bottom (triggerfish are demersal spawners despite their large size). Eggs are scattered and attached to sand particles. Triggerfish eggs are usually very small (diameter of 0.5–0.6 mm) and are easily spread by waves. After spawning, both the male and female participate in caring for the fertilized eggs (biparental egg care). A female triggerfish stays near the spawning ground, around 5 m off the bottom, and guards the eggs within her territory against intruders. Some common intruders include '' Parupeneus multifasciatus, Zanclus cornutus, Prionurus scalprum'', and conspecifics. Besides guarding, females roll, fan, and blow water on eggs to provide oxygen to the embryos, thereby inducing hatching. This behavior of female triggerfish is called "tending", and males rarely perform this behavior. A male triggerfish stays farther above the eggs and guards all the females and eggs in his territory. Males exhibit aggressive behaviors against conspecific males near the boundaries of their territories.

Mating systems

In crosshatch triggerfish ('' Xanthichthys mento'') and yellow margin triggerfish ('' Pseudobalistes flavimarginatus''), eggs are spawned in the morning and they hatch after the sunset on the same day. After hatching of embryos, the female crosshatch triggerfish leaves the male's territory. This mating system is an example of male-territory-visiting

polygamy Crimes Polygamy (from Late Greek (') "state of marriage to many spouses") is the practice of marriage, marrying multiple spouses. When a man is married to more than one wife at the same time, sociologists call this polygyny. When a woman is ...

. Triggerfishes exhibit other types of mating systems, as well, such as a nonterritorial-female (NTF) polygyny and territorial-female (TF) polygyny. In NTF polygyny, nonterritorial females stay in the male's territory and reproduce. In TF polygyny, a female owns territory within a male's territory and will spawn in her territory.

Life history

Triggerfish lay their demersal eggs in a small hole dug in the sea bottom. Off

Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and to ...

, juveniles of some species of triggerfishes are found in floating ''

Sargassum ''Sargassum'' is a genus of brown (class Phaeophyceae) macroalgae ( seaweed) in the order Fucales. Numerous species are distributed throughout the temperate and tropical oceans of the world, where they generally inhabit shallow water and coral ...

'', where they feed on the small shrimp, crabs, and mollusks found there.

Edibility

Some species of triggerfish, such as the titan triggerfish, may be ciguatoxic and should be avoided. Others, however, such as the grey triggerfish (''Balistes capriscus''), are edible.

Gallery

File:Reef Triggerfish 1.JPG, The reef triggerfish is the state fish of Hawaii. File:Balistapus undulatus.jpg, Most triggerfish are aggressive, but few match the orange-lined triggerfish. File:2005-03-01 - Gilded triggerfish.jpg, The gilded triggerfish is among the few

sexually dimorphic Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...

triggerfish. The female lacks the blue throat and yellow fin-edging. File:Redtoothed triggerfish.jpg, The redtoothed triggerfish is one of the relatively few

planktivore A planktivore is an aquatic organism that feeds on planktonic food, including zooplankton and phytoplankton. Planktivorous organisms encompass a range of some of the planet's smallest to largest multicellular animals in both the present day and i ...

s of the family. File:4987 aquaimages.jpg, The queen triggerfish has elegant extensions to its fins. File:Sargassum triggerfish Xanthichthys ringens.jpg, Adult sargassum triggerfish live around

reef A reef is a ridge or shoal of rock, coral or similar relatively stable material, lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic processes— deposition of sand, wave erosion planing down rock o ...

s and

banks A bank is a financial institution that accepts deposits from the public and creates a demand deposit while simultaneously making loans. Lending activities can be directly performed by the bank or indirectly through capital markets. Becaus ...

, but juveniles live around

sargassum ''Sargassum'' is a genus of brown (class Phaeophyceae) macroalgae ( seaweed) in the order Fucales. Numerous species are distributed throughout the temperate and tropical oceans of the world, where they generally inhabit shallow water and coral ...

References

External links

* * * {{Authority control Tetraodontiformes Extant Eocene first appearances