Pearlfish

Pearlfish are marine fish belonging to the family Carapidae and are found in tropical waters of the Atlantic, Indian, and Pacific Oceans at depths up to 2,000 meters. They inhabit oceanic shelves and slopes and are characterized by their slender, elongated bodies, lack of scales, and translucent appearance. Their dorsal fin rays are shorter than their anal fin rays, and the largest species can reach up to 50 cm in length. Pearlfish reproduce by laying oval-shaped eggs approximately 1 mm in length.

Most adult pearlfish live symbiotically inside various invertebrates, such as clams, sea cucumbers, starfish, or sea squirts. While some species are commensal and do not harm their hosts, others are parasitic, feeding on the gonads and internal organs of sea cucumbers. Adults typically live alone or in pairs. In contrast, pearlfish larvae are free-living and can be identified by a long filament near their dorsal fins, sometimes with additional appendages.

The family Carapidae is divided into three genera based on their symbiotic relationships: Echiodon and Snyderidia, which are free-living; Carapus and Onuxodon, which are commensal; and Encheliophis, which are parasitic and often found in shallow-water coral communities. These fish inhabit hosts such as bivalves, sea cucumbers, and starfish.