TRIGGERFISH: CHARACTERISTICS, HABITAT, FEEDING, BEHAVIOR - BIOLOGY - 2024

Triggerfish is the common name for any of the species of fish that make up the Balistidae family. Among its most representative features are its eyes, which can rotate them independently.

In addition, it has two dorsal fins, the previous one being reduced to three spines. The first of these, which is the largest of all, rises and is supported by the second. In this way, the fish looks more aggressive, so that predators flee or are unable to catch it.

Trigger fish. Source: Arpingstone

Their diet is very diverse, including sea urchins, crustaceans and mollusks. To grind the shells and spines, the triggerfish has a strong jaw and specialized teeth.

In relation to its distribution, triggerfish, as this species is also known, inhabit tropical and subtropical oceans worldwide. However, the highest species richness occurs in the coral reefs of the Indo-Pacific.

characteristics

Skin

The skin is very thick and hard. It is covered with large, rough and non-overlapping scales, thus forming a strong armor that protects the body. Regarding the coloring, it is very varied. Generally, triggerfish can be brown, black, greenish, or gray, with striking patterns of bright colors.

Size

This species can measure between 20 and 50 centimeters. However, there are large fish, such as the stonefish (Pseudobalistes naufragium), which can reach a length of one meter.

Head

The head is large and at its end is the mouth. This is small and contains two strong jaws. Each of these bone structures has a row of four teeth on each side. However, in the upper jaw there is a set of pharyngeal teeth, which form a plaque.

These teeth are adapted to grind hard-shelled prey. As for the eyes, they are small, in relation to the body, and are located in the upper area of ​​the head. A peculiarity of this species is that it has the ability to independently rotate each eyeball.

Fins

The triggerfish has two dorsal fins. The first is reduced to three spines, the first being the longest and most robust of all. From this group of thorns, the first two can be raised. The first is held firmly upright, because the second spine, when erect, blocks it, thus holding it tightly.

This action is a protection mechanism, which prevents the predator from ingesting it. In addition, it contributes to their appearance look more threatening.

The vast majority of the rays that make up the pectoral, anal and dorsal fins are branched. In relation to the two pelvic fins they are rudimentary. These are fused to a column, represented by four pairs of large scales, which cover the pelvis at its posterior end.

As for the caudal fin, it is sickle-shaped and consists of a total of twelve main rays and lacks spines.

Gill plates

The group of species that make up the Balistidae family have operculum, known as gill plates. This structure is in charge of protecting the gills, whose only opening is located in front of the base of the pectoral fin.

In triggerfish, the gill plates are not very visible, as they are superimposed by the tough skin of the animal.

The swim

This group of fish generally swim by simultaneously waving their anal fins and second dorsal fin. In these species, these fins are slightly inclined towards each other, so the odes produce a forward thrust. This wave motion provides a slow movement and constitutes its main mode of propulsion.

When it needs to escape a threat, the fish uses the tail fin, which can extend up to 2.5 times its width, forming a kind of fan. In this way, it provides strong propellant blows, which generate a fast and powerful impulse.

Some species have very particular swims. Such is the case of the Balistapus aculeatus, which has the ability to swim backwards, by reversing the usual direction of the undulations in both fins.

In addition, it can move down in the water, since the anal fins generate waves backwards and the dorsal one does it forward. When you want to scroll up, this species changes both wave directions. In this video you can see a triggerfish attacking a lobster:

Habitat and distribution

Hogfish, as members of this family are commonly named, are widely distributed in tropical and subtropical waters worldwide. However, the highest population density occurs in the tropical Indo-Pacific region.

In relation to the habitat, it varies according to the species. Some live and reproduce in areas close to coral reefs, at depths between 50 and more than 100 meters. In that area, they usually use crevices or rocks to hide at night, thus avoiding being seen by predators.

Other species, such as those that make up the genus Canthidermis, are fundamentally pelagic, inhabiting open waters. However, some triggerfish, despite being pelagic or benthic, can live at different depths at a certain time in their life.

Thus, the Canthidermis maculata, which is epipelagic during most of its life, the adult descends to shallow waters during the spawning season. In the case of Balistes polylepis, which is located on rocky reefs, in the juvenile stage it is pelagic, while as an adult it is demersal.

State of conservation

Some of the populations that make up the Balistidae family are declining. Because of this, the IUCN have categorized them within the group of species at risk of extinction. Among the triggerfish that make up this red list are Canthidermis maculata, Balistes capriscus and Xanthichthys mento.

There are various factors that affect these communities. These include bycatch, which occurs during the tuna fishery. Also, triggerfish is overexploited in various regions, especially in Brazil, the Gulf of Mexico and the Gulf of Guinea.

On the other hand, because their preferred habitat is coral reefs, in several areas the ecosystem is degraded by water pollution, overfishing, and coral bleaching.

Feeding

The Balistidae family is made up of more than 40 different species, so their diet is very varied. However, their diet is generally based on mollusks, crustaceans, sea urchins and other echinoderms.

Another group hunts small fish, while some, including members of the genus Melichthys, primarily feed on algae.

Also, there are them with specialized diets, as is the case of the red-toothed hog (Odonus niger), which feeds mainly on marine plankton.

The triggerfish has several hunting methods. It can capture its prey using its teeth, thus ensuring that it does not escape. Also, when the dam is covered in sand, it creates a stream of water, vigorously flapping its fins. In this way, the animal is exposed and can be easily captured.

This technique, known as jet of water, is used by the Balistes vetula when hunting sea urchins. The force of the water that this fish generates overturns the hedgehog, making it vulnerable, since in the lower part of its body the spines are short and it can be easily predated.

Reproduction

The male triggerfish establishes his territory for spawning and caring for the eggs. In this there are between one and three females. During the reproductive season, it exhibits courtship behaviors. Thus, it repeatedly chases females that pass near it.

Mating occurs on the sandy bottom or on a reef. Regarding spawning, the female releases between 55,000 to 430,000 eggs. Because they are in pairs, the male immediately expels the sperm, which fertilize the eggs. Because these are adhesive, they bond with the sand.

In some species, the fertilized eggs are scattered on the bottom, while in others they form a kind of mass. Regarding parental care, in the vast majority of cases, the female is in charge of protecting the eggs.

To do this, they fan and blow water on the fertilized eggs, in addition to warding off intruders. Also, the male can participate in these tasks, but such behavior is rare within the populations of this fish.

Behavior

Many of the hogfish are solitary. Although their appearance is docile, some become very aggressive during the reproductive season. This is because they become territorial as they fiercely defend the nest.

Regarding communication, the species of the family Balistidae are known for their great ability to produce sounds. Some are emitted during feeding, as a product of the collision between the teeth.

In other species, such as B. capriscus, the sounds result when the first spine of the dorsal fin rises. However, recent studies indicate that the vast majority of sounds involve the pectoral fins and the swim bladder. This organ has lateral expansions that join the pectoral fins to the wall of the body.

Thus, in this area, the swim bladder acts as a drum membrane. The production of the tapping is given by the alternating sweeping movements of the pectoral fins, against the wall of the swim bladder.

References

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7. Eric Parmentier, Xavier Raick, David Lecchini, Kelly Boyle, Sam Vanwassenbergh, Frédéric Bertucci, Loïc Kéver (2017). Unusual sound production mechanism in the triggerfish Rhinecanthus aculeatus (Balistidae). Recovered from jeb.biologists.org.
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9. T‐ Chen RFG Ormond H ‐ K. Mok (2005). Feeding and territorial behavior in juveniles of three co ‐ existing triggerfishes. Recovered from onlinelibrary.wiley.com.