Quick referenceBrooklynella hostilis is an aggressive ciliate parasite that strikes newly-imported clownfish. Causes excess slime coat + rapid breathing. Treat with formalin baths immediately.
Symptoms
Excess slime coat (cloudy/sloughing)
Rapid breathing
Surface gasping
Refusing food
Lethargy
Color fade
Skin sloughing in patches
Cause
Brooklynella hostilis ciliate. Strikes recently-shipped or wild-caught clownfish (especially A. ocellaris + A. percula imports). Stress-triggered. Less common in captive-bred fish.
Treatment options
Formalin bath (37%). CRITICAL TREATMENT. 45-minute bath in 1 tsp formalin per 1 gal aerated saltwater. Use plastic bucket, vigorous airstone. Single bath often enough; repeat in 48h if symptoms persist.
Drop fresh water bath. Backup if formalin unavailable. 10-minute pH-matched freshwater bath. Less effective; only use if formalin not available.
Quarantine + observe. House treated fish in clean QT for 30 days. Monitor for relapse.
Improve water quality. Ensure ammonia 0, nitrite 0. Stress + poor water make brookly worse.
Always treat in a separate quarantine or hospital tank. Most medications are toxic to coral, invertebrates, and live rock biology. Consult an aquatic veterinarian for valuable fish.
Prevention
Buy captive-bred clownfish (Sustainable Aquatics, ORA, Bali Aquarich). Always quarantine wild + imported clownfish 30+ days. Drip acclimate slowly. Do not skip QT for "small batch" arrivals.
Fatality + outcome
Very high without treatment - kills clownfish in 24-72 hours. Aggressive, fast-progressing.