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Parasitic

Brooklynella

Brooklynella hostilis
Also called: Clownfish disease, Brook
CriticalSaltwaterContagious
Not veterinary advice. Symptoms overlap between conditions and a wrong treatment can make things worse. Consult an aquatic vet for valuable specimens or anything not responding to standard treatment.
Healthy Ocellaris clownfish (Amphiprion ocellaris) — the most affected species. Wild-caught and freshly-imported clownfish develop Brooklynellosis under transport stress: thick gray-white mucus that peels and sheds in visible sheets across the head and gills, often within 24 hours of stocking. Photographic references of active outbreaks are kept in hobbyist quarantine threads on Humble.Fish and Reef2Reef rather than open archives.Host species
Healthy Ocellaris clownfish (Amphiprion ocellaris) — the most affected species. Wild-caught and freshly-imported clownfish develop Brooklynellosis under transport stress: thick gray-white mucus that peels and sheds in visible sheets across the head and gills, often within 24 hours of stocking. Photographic references of active outbreaks are kept in hobbyist quarantine threads on Humble.Fish and Reef2Reef rather than open archives.
Hobgood, N. (n.d.). Amphiprion ocellaris (Clown anemonefish) [Photograph]. Wikimedia Commons. CC BY-SA 3.0.

Symptoms

Excess mucus production, fish develops a cloudy, peeling, gray-white slime coat that sloughs off in sheets. Rapid breathing, gasping at the surface, lethargy, refusing food. Often presents first in newly-imported clownfish, especially wild-caught Maroons and Tomatoes. Mortality is high and fast, 24-48 hours from first symptoms is common.

Causes

A ciliated protozoan that attacks the skin and gills. Spreads quickly between fish via direct contact and the water column. Strongly associated with the stress of capture, transport, and acclimation in newly-imported clownfish. Wild-caught fish carry it asymptomatically until stress triggers an outbreak.

Treatment

Formalin baths or formalin tank treatment is the gold standard, typically 45-minute dips in heavily-aerated water at the label concentration. Repeat every 2-3 days for 2 weeks. Methylene blue can be added to formalin baths for extra antibacterial protection. Heavy aeration is critical, formalin reduces oxygen significantly. Hospital tank only, formalin nukes filtration and is toxic to invertebrates.

Prevention

Quarantine all newly-imported clownfish, especially wild-caught. Captive-bred clownfish from reputable breeders rarely carry Brooklynella. If you must buy wild-caught, plan a prophylactic formalin dip during QT.

Notes

Easily confused with Marine Velvet, both produce mucus issues and rapid breathing. Brooklynella mucus is thicker and visibly sheds; Velvet looks like gold dust. When in doubt and clownfish are involved, treat for Brooklynella first.