Skin Flukes (Gyrodactylus): symptoms, treatment, prevention

Gyrodactylus spp. are live-bearing monogenean flukes that attach to skin and fins via a hooked posterior haptor and multiply rapidly on stressed fish.

Overview

Skin Flukes are caused by Gyrodactylus spp., monogenean parasites that reproduce by viviparity. A single attached worm can rapidly produce a cascading population on stressed fish, leading to skin damage and secondary infection.

Symptoms

• Frayed and irritated fins
• Flashing on substrate
• Excess body slime
• Small hemorrhagic spots
• Clamped fins
• Weight loss

Causes

Introduction with new fish (low-level infestations are common in shop stock) and direct contact spread. Stress, poor water quality and crowding allow viviparous multiplication.

Diagnosis

Persistent flashing and frayed fins, with no white spots, point to flukes. Microscopy of a skin scrape shows the characteristic hooked haptor and embryos visible inside the parent, distinguishing Gyrodactylus from Dactylogyrus (gill predilection, eggs not embryos) and from Ich.

Treatment

Praziquantel is the first-line treatment; it is reef-safe and effective against viviparous monogeneans. Severe outbreaks may need a formalin bath in quarantine.

Quarantine

Praziquantel can be dosed in the display tank for most species. For severe cases or marine systems with sensitive corals, move fish to a hospital tank and treat there.

Medication

1. Praziquantel at 2.5 mg/L in the tank for 5-7 days; broadly safe for fish, plants and most invertebrates.
2. Formalin bath at about 150 ppm for ~60 minutes in quarantine with strong aeration; repeat after 5 days if needed.

Recovery

Generous water changes and good nutrition restore the slime coat. Watch for secondary bacterial fin rot at damaged sites and treat early if it appears.

Prevention

• Quarantine new fish
• Praziquantel prophylaxis in quarantine
• Minimise stress
• Maintain good water quality