A novel approach using vinegar to eradicate recalcitrant skin flukes in koi fish: a case report

Skin flukes (Gyrodactylus) are common primary ectoparasites of fish, particularly in koi kept by hobbyists. Gyrodactylus cause severe skin and gill damage as they move and graze on the fish's mucus and epithelium. Fish respond to the irritation by flashing (scratching their flanks against objects and substrate). Untreated fluke infestations lead to skin ulceration, secondary bacterial infections and potential death. The parasites enter ponds and aquariums most commonly when infected fish are introduced, and can also be introduced by contaminated equipment, plants and water. These parasites accumulate and amplify in recirculating ponds, especially in ponds with high densities of fish. The first clinical signs of disease can be observed within 1 week in warm water temperatures (22–26°C) or within a month in cooler water temperatures (8–15°C).

Unlike gill flukes (Dactylogyrus), which are oviparous, skin flukes are viviparous trematodes. Eradication of skin flukes is often achievable using a single dose of treatment, as they lack a drug-re-sistant egg-stage. However, in practice, achieving eradication can be hindered by poor distribution of medicines around the aquatic system if plants or pond furnishings obstruct drug dispersal, rapid degradation of medications (ultraviolet steriliser, water chemistry, bacterial degradation, chemical filtration, photoinactivation, temperature) and drug resistance.