Pinecone fishes are small and unusual marine fish of the family ''Monocentridae''. The family contains just four species in two

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...

, one of which is monotypic. Their distribution is limited to tropical and subtropical waters of the

Indo-Pacific The Indo-Pacific is a vast biogeographic region of Earth. In a narrow sense, sometimes known as the Indo-West Pacific or Indo-Pacific Asia, it comprises the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the ...

. Pinecone fishes are popular subjects of public aquaria, but are both expensive and considered a challenge for the hobbyist to maintain.

Description

These fish are aptly named; their rounded, compressed bodies are completely covered (with the exception of the caudal peduncle) with very large, strong, platelike

scale 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 ...

s called scutes, which are fortified with prominent ridges. The first dorsal fin is composed of four to seven strong, disunited spines which vary in length; the second dorsal fin and

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 ...

are small, spineless and rounded, situated far back of the convex head. The pectoral fins are somewhat elongate and the caudal fin is truncate. Coloration is typically a yellow to orange, with the scales dramatically outlined in black. The eyes are relatively large, and the mouth is oblique and subterminal. On either side of the lower jaw is a

bioluminescent Bioluminescence is the production and emission of light by living organisms. It is a form of chemiluminescence. Bioluminescence occurs widely in marine vertebrates and invertebrates, as well as in some Fungus, fungi, microorganisms including ...

organ called a photophore: a pale light is produced by

symbiotic Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

bacteria within the organ, and the color of the light varies with ambient light levels—orange by day and blue-green at night. The pineapplefish, ''Cleidopus gloriamaris'', is the largest species, reaching up to in length. Sexual dimorphism is not apparent.

Life history

Pinecone fishes inhabit the sublittoral zone, and are associated with ledges and caves, rocky and (occasionally) coral reefs over a hard bottom. Found at 10–200 m deep (with juveniles frequenting the shallower end of this range), pinecone fishes are

nocturnal Nocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite. Nocturnal creatures generally have highly developed sens ...

and form schools. The photophores are thought to play a role in attracting the zooplankton upon which the fish feed; intraspecific communication may also be a use for the light. Little is known of their reproductive biology, but they are assumed not to guard their brood.

References

{{Taxonbar, from=Q1550938 Bioluminescent fish Ray-finned fish families Taxa named by Theodore Gill