Dactylogyrus

Dactylogyrus is a genus of ectoparasitic flatworms in the family Dactylogyridae, within the class Monogenea of the phylum Platyhelminthes. They are monogenean parasites that colonize the gills of freshwater fish, notably cyprinids such as carp, goldfish, and koi, as well as some ornamental species. Species within the genus are generally host-specific and can occur in single or mixed infections.

Biology and life cycle: Dactylogyrus species have a direct life cycle. Adults attach to the gill filaments using specialized posterior clamps (the haptor). They reproduce sexually and produce eggs that exit with the water, hatching into free-swimming oncomiracidia that locate a host fish and attach to the gills. Development time is temperature dependent and can range from about a week to several weeks. There is no intermediate host.

Pathology: Heavy infestations irritate the gills, causing increased mucus production, flashing, and respiratory distress. Secondary infections and reduced growth are common in heavily infected fish, particularly under stressful conditions.

Diagnosis and management: Diagnosis relies on observation of parasites on gills or in gill scrapings, with identification aided by morphology of the attachment organs and reproductive structures. Management includes quarantine of new fish, maintaining high water quality, and treating with antiparasitics such as praziquantel, formalin, or copper-based products, following veterinary or supplier guidance. Because free-swimming larvae can re-infest, treating all fish and environmental reservoirs is often necessary.

Taxonomy and notes: Dactylogyrus comprises many species with various host ranges; they are among the most common gill parasites in aquaculture and ornamental fish.