Louseflukes

Louseflukes are a group of external parasites belonging to the Monogenea class, a subclass of parasitic flatworms. These organisms are typically found attached to the gills, fins, or skin of fish. Their common name derives from their superficial resemblance to lice, though they are not closely related. Louseflukes are characterized by their direct life cycle, meaning they do not require intermediate hosts. They reproduce sexually, and their eggs hatch into free-swimming larvae that must find a new host to attach to and mature.

The attachment of louseflukes to their fish hosts is facilitated by specialized structures called haptors, located at the posterior end of the worm. These haptors are equipped with hooks, clamps, or suckers that allow the parasite to anchor itself firmly. Feeding typically involves scraping epithelial cells or feeding on mucus and blood. Heavy infestations can cause significant stress to the host, leading to skin lesions, secondary bacterial infections, and even death, particularly in aquaculture settings where fish are kept at high densities. Diagnosis is usually made by visual inspection of the fish or by microscopic examination of scrapings from the skin or gills. Treatment often involves chemical dips or baths designed to kill the parasites without harming the host fish.