Philometrids

Philometrids are a family of parasitic nematodes belonging to the order Spirurida. These nematodes are endoparasites, primarily infecting fish and occasionally other aquatic vertebrates. They are known for their characteristic long, thread-like bodies and their presence within the host's tissues, often in the musculature, subcutaneous tissue, or associated with organs.

The life cycle of philometrids typically involves an aquatic intermediate host, such as copepods or other small invertebrates, which ingest the infective larval stages. When a suitable definitive host consumes the infected intermediate host, the parasite matures within its tissues. Adult female philometrids are notably larger than males and are often found embedded in the host's body. The females release their eggs or larvae into the host's tissues or body cavities, from where they may be released into the environment upon the host's death or excretion.

Parasitism by philometrids can cause a range of pathological effects in their hosts, depending on the species of nematode and the intensity of infection. These effects can include inflammation, tissue damage, the formation of granulomas, and reduced growth or reproductive capacity in heavily infected individuals. While some philometrid infections are asymptomatic, others can lead to visible nodules or lesions on the host. They are of interest to fisheries due to their potential impact on fish health and aquaculture.