Carapus

Carapus is a genus of fish in the family Carapidae, commonly known as pearlfish or carapid eels. These elongated, eel-like fish are found in tropical and subtropical seas worldwide. They are characterized by their translucent bodies, often lacking scales, and their ventral fins are typically fused into a single sucker-like structure. Carapus species are primarily known for their commensal relationship with other marine invertebrates, most notably sea cucumbers and bivalves. They often inhabit the body cavities or respiratory trees of these hosts, feeding on parasites or the host's gonads. This association is generally considered harmless to the host, though there can be exceptions. The life cycle of Carapus species involves a larval stage that is pelagic before settling into a host. Reproduction typically occurs within the host. Their diet varies depending on the species and host, but often includes small crustaceans, polychaetes, and the eggs or gonads of their hosts. They are not commercially important fish, and much of their biology remains poorly understood due to their secretive lifestyle.