Rhinecanthus aculeatusLagoon humu(Also: Lagoon triggerfish; striped triggerfish)

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Geographic Range

Considered to live in the Indo-Pacific region, reef triggerfish transverse a wide variety of marine areas from thirty degrees north to south in latitude (Michael 1998). Reef triggerfish extend from the Hawaiian islands southward to Polynesia and Australia, westward through Micronesia and Melanesia, through the East Indies including the Philippines, across the Indian Ocean, to the coast of Africa and the Red Sea. More specifically, reef triggerfish occupy the Red Sea south to South Africa, east to the Hawaiian, Marquesas, and Tuamotu Islands, north to southern Japan, south to Lord Howe Island, Micronesia, and the Eastern Atlantic from Senegal to South Africa (Allen and Steen 1994).

Habitat

The reef triggerfish is generally found in shallow outer reef habitats. Swimming along the bottom in search of food items, it is found on surge-swept basalt reefs. The reef triggerfish is commonly found in subtidal reef flats and protected lagoons (Hoover 1993). This marine fish usually occupies water with salinity levels ranging from 1.020 to 1.023, and water temperatures from seventy-seven to eighty degrees Fahrenheit (Tinker 1982).

Physical Description

A reef triggerfish is easily distinguished by its angular body, distinctive color pattern (resembling blocks of colors), fin arrangement, and characteristic dorsal spine. This forward spine on the dorsal fin lies slightly above and behind the eye. It is very strong and rigid, serving as defense adaptation. When this spine is raised, it often locks in this protective position, giving the triggerfish its name. Altogether, there are three dorsal spines, twenty-three to twenty-six dorsal softrays, twenty-one to twenty-three anal softrays, and no anal spines (Michael 1998). Considered to be sturdy and well-built, the reef triggerfish reaches a maximum length of thirty centimeters (Tinker 1982). It has a small but powerful jaw, equipped with sharp, cutting teeth. The eyes of a reef triggerfish are set atop the head, moving independently, so as to scan the reef for possible predators and prey (Hoover 1993).

Reproduction

Like most fishes, the reef triggerfish undergoes heterosexual reproduction, in which there are separate male and female parents. Reef fishes are egg-layers, and the eggs are externally fertilized by the male parent. Nests are built by the female parent, in which the eggs are fertilized and cared for until they hatch. The newly-hatched young are also looked after by the female parent (Hoover 1993).

Behavior

The reef triggerfish swims in a very characteristic manner, propelling itself through the water using waving motions of the broadened dorsal and anal fins, allowing it great maneuverability. The reef triggerfish has the ability to move forward, backward, or hover above the reef. The presence of a strong, broom-like tail allows the reef triggerfish to dash quickly into the reef when confronted with danger (Michael 1998). When encountering predators, reef triggerfish utter grunting noises. It has been speculated that these sounds work to warn other triggerfish of the present danger (Dresie 1999). When retreating to the reef in response to danger, a reef triggerfish wedges itself into a hole by raising the large dorsal spine. A second, smaller dorsal spine locks the first in place. Yet another anal spine helps the fish to enter the shelter. This behavior is also often utilized at night, as a reef triggerfish wishes to rest within a reef. When resting, the reef triggerfish sleeps on its side (Waikiki Aquarium Education Department 1999). Considered to be one of the more aggressive of the triggerfish, the reef triggerfish also often displays this aggression toward members of its own species in addition to other fish that are similar in size. The territorial reef triggerfish often emits a whirring soung when startled. It is not easily approachable and keeps a fair distance from other organisms. The vocal reef triggerfish has the ability to make a snorting noise when brought to the surface, as its defensive puffing technique is reduced. This unique ability has given the reef triggerfish its Hawaiian common name of Humu-humu-nuku-nuku-apu'a, which directly translates to "Fish who comes out of the water and sounds like a pig" (Animal World 2000).

Communication and Perception

Food Habits

The reef triggerfish diet consists mainly of reef invertebrates and algae. Common food items are small crustaceans, worms, brittlestars, sea urchins, and snails. Less common dietary supplements are other fishes, corals, tunicates, forams, and eggs. Highly versatile in its feeding possibilities, the reef triggerfish will feed on a wide variety of crustaceans, molluscs, and fish. Reef triggerfish obtain their food primarily by rooting through sand or rocks (Animal World 2000; Tinker 1982).

Economic Importance for Humans: Positive

Caught with drive-in nets, reef triggerfish satisfy minor commercial fisheries purposes, but have a high commercial value for aqauriums. Reef triggerfish are considered good aquarium fish, as they are hardy and easy to keep and maintain. The ability of the fish to feed upon a wide variety of items, from live to frozen and flake foods, makes it very marketable among aquariums. With no special requirements for temperature or light conditions, the reef triggerfish is relatively versatile in its ability to adapt to environmental conditions. As it is easily caught and therefore readily available for purchase, the reef triggerfish is popular, also due to its unusual markings and vibrant color (Waikiki Aquarium Education Department 1999). The reef triggerfish also has a good disposition relative to other kinds of triggerfish. The reef triggerfish is not currently highly valued as a commercial food item for the majority of the human population. However, early Hawaiians ate it infrequently. The fish was also dried and utilized as a cooking fuel by early Hawaiians when other sources of fuel were in short supply. More importantly, the reef triggerfish was used further as a substitute for pigs for some religious ceremonies (Hoover 1993).

Conservation Status

Currently abundant in many marine environments, the reef triggerfish is not presently at risk. However, major alterations are occurring in many of these habitats, carrying the potential to greatly reduce their numbers. In additon to tropical fish collectors, human population growth and the factors that accompany it pose threats to reef triggerfish, as well as other marine fishes and organisms. Though currently not at risk, other organisms in many of the reef triggerfish's habitats are being greatly reduced by abiotic factors (Dresie 1999).

Other Comments

In 1984-85, the reef triggerfish was voted the official State Fish of Hawaii, as it is historical for the state, and is one of the most abundant and widely recognized Hawaiian fishes. The official term of office lasted for five years, and upon its culmination there was no re-election campaign. Though the reef triggerfish was not re-elected into office, it remains the unofficial State Fish of Hawaii. Hawaiians have given the reef triggerfish the common name of Humu-humu-nuku-nuku-apu'a (Waikiki Aquarium Education Department 1999). Also widely known as the Picasso triggerfish, the reef triggerfish shares its scientific name with its less common relative, the lagoon triggerfish (Michael 1998).

Contributors

William Fink (editor), University of Michigan-Ann Arbor.

Karla Schaffer (author), University of Michigan-Ann Arbor.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

reef

structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.

tactile

uses touch to communicate

References

2000. "Animal World" (On-line). Accessed October 30, 2000 at http://animalatlas.com/encyclo.

1999. "Waikiki Aquarium Education Department" (On-line). Accessed October 28, 2000 at http://waquarium.mic.hawaii.edu.

Allen, G., R. Steene. 1994. Indo-Pacific Coral Reef Field Guide. Singapore: Tropical Reef Research.

Dresie, D. 1999. "Let's Go Shore Dive'N' on the Kona Coast" (On-line). Accessed October 30, 2000 at http://lehua.ilhawaii.net/~dpdresie.

Hoover, J. 1993. Hawaii's Fishes, A Guide for Snorkelers, Divers, and Aquarists. Honolulu, HI: Mutual Publishing.

Michael, S. 1998. Reef Fishes, Volume 1: A Guide to Their Identification, Behavior, and Captive Care. Shelburne, Vermont: Microcosm Limited.

Tinker, S. 1982. Fishes of Hawaii. Honolulu, HI: Hawaiian Service Incorporated.