Philometrid

A philometrid is a type of parasitic nematode belonging to the family Philometridae. These roundworms are characterized by their slender, thread-like bodies and often inhabit the tissues of fish. A notable feature of philometrids is that the adult females are significantly larger than the males, and the females often reside within the host's body cavity, particularly in the gonads or subcutaneous tissues, for extended periods. The males are typically found in the female's reproductive tract or the surrounding host tissue.

The life cycle of philometrids is complex and often involves an indirect route, with intermediate hosts playing a role in transmission. Small invertebrates, such as crustaceans, frequently serve as intermediate hosts, ingesting the parasite's larval stages. Fish then become infected by consuming these infected intermediate hosts. Once inside the fish, the larvae mature into adult worms. Philometrid infections can cause various pathological effects in fish, ranging from reduced reproductive success to visible abnormalities, depending on the species of worm and the host. Diagnosis is usually made by observing the characteristic adult females, which can be quite prominent, often protruding from the host's body or visible upon dissection.