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Pinecone fishes are small and unusual marine fish of the family Monocentridae. The family contains just four species in two genera, one of which is monotypic. Their distribution is limited to tropical and subtropical waters of the Indo-Pacific. Pinecone fishes are popular subjects of public aquaria, but are both expensive and considered a challenge for the hobbyist to maintain.

Appereance[]

These fish are aptly named; their rounded, compressed bodies are completely covered (with the exception of the caudal peduncle) with very large, strong, platelike scales 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 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 organ called a photophore: a pale light is produced by symbiotic 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 30 cm (12 in) 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 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.

The scales of the Pineapplefish are very strong and like an armor which helps to protect the fish from predators like large reef.

Japanese pineapplefish[]

Monocentris japonica, the Japanese pineapplefish, is a pinecone fish of the family Monocentridae, found in the tropical Indo-West Pacific Oceans, at depths between 2 and 100 m and can be found on both rocky and coral reefs. The fish is nocturnal and shelters in caves and under ledges during the day.

Appereance[]

The pineconefish is yellow with distinct large scales outlined in black. It has light-producing organs filled with luminescent bacteria on each side of the lower jaw, the purpose of which is not known, but may help it to see at night or to attract prey. The fish grows to 17 cm, but is more commonly found up to 12 cm.

Pinecone fish do not have scales, and are instead covered in scutes. Scutes are similar to scales and serve the same function. Unlike the scales of fish, which are formed from the epidermis, scutes are formed in the lower vascular layer of the skin and the epidermal element is only the top surface. Forming in the living dermis, the scutes produce a horny outer layer, that is superficially similar to that of scales.

Scute comes from Latin for shield, and can take the form of:

  • An external shield-like bony plate, or
  • A modified, thickened scale that often is keeled or spiny, or
  • A projecting, modified (rough and strongly ridged) scale, usually associated with the lateral line, or on the caudal peduncle forming caudal keels, or along the ventral profile.

In captivity[]

Pinecone fish are often kept by aquarists because they are not aggressive and easy to keep. In aquaria, they are usually fed fresh marine foods or brine shrimp.

Species-based characters[]

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