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Squirrel Fish

Squirrel fish, belonging to the order Beryciformes, are brightly colored, medium-sized fish that are active mostly at night. Squirrel fish live in rocky or coral reefs in tropical and warm temperate seas. Their most distinguishing characteristics are their large eyes and their ability to make sounds to ward off intruders.

The order Beryciformes is composed of 15 families and about 150 species of marine fish, including squirrel fishes, whalefishes, lanterneyes, and slimeheads. The fish classified within this order are widely varied and, in the past, have been placed in separate orders; in fact, their relationship is still debated. Most of the order's 15 families contain fewer than a dozen species; however, the family in which squirrel fishes are classified, Holocentridae, is the largest. It contains about 70 species.

The Holocentridae family is further divided into two subfamilies: Holocentrinae (squirrel fishes) and Myripristinae (soldierfishes). Until recently, the subfamily of squirrel fishes was thought to contain only one genus, Holocentrus. But, two new species having significant anatomical differences were found in the Atlantic. Thus, they were given separate genera, Flammeo and Adioryx. These three genera contain a total of 32 species of squirrel fish.

A school of squirrel fish in the Caribbean. Photograph by Stephen Frink. Stock Market. Reproduced by permission.

All squirrel fish have large eyes, and they often measure between 12-24 in (30-60 cm) long. These fish are commonly brightly colored—usually red—which helps them blend into their bright environment, the coral reef. Some squirrel fish also have stripes. Their bodies are covered with large, rough scales and sharp spines.

Squirrel fish are nocturnal; thus, they hide in crevices or underneath rocky surfaces in coral reefs during the daytime. At night, they spread out over the reef looking for food. While some species of squirrel fish can go as deep as 660 ft (200 m), most species are found in fairly shallow water, usually between the surface and 330 ft (100 m) deep. Adults stay close to the bottom, but the young commonly float nearer to the surface.

Squirrel fish are known for their ability to make a variety of clicking and grunting noises, produced by vibrating their swim bladders. It is believed that they do this to defend themselves and their territories. For example, one species, the longspine squirrel fish, is believed to make different sounds depending on the type of threat that is faced. The longspine uses a single grunt when challenging another fish that presents little threat. However, when facing a fish that is too large to intimidate, the longspine emits a series of clicking noises, signaling the need to retreat from the situation. The longjaw squirrel fish has also been observed making similar noises.

Squirrel fish are sometimes eaten by humans; but because they are relatively small and covered with rough scales and spines, they have very little commercial value.

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Science EncyclopediaScience & Philosophy: Spectroscopy to Stoma (pl. stomata)