Brooklynella - the clownfish killer.

What is Brooklynella

Brooklynella hostilis is a ciliated protozoan parasite that targets the skin and gills of marine fish, with a strong preference for clownfish - especially wild-caught Amphiprion species. Unlike ich (which embeds as visible white spots) or velvet (which produces a gold sheen), Brooklynella manifests as excess mucus production, peeling skin, and rapid breathing. By the time symptoms are obvious, mortality is often hours away.

The disease earned the nickname "clownfish disease" because clownfish are uniquely susceptible. Other marine fish can carry Brooklynella without symptoms; clownfish develop full clinical infection rapidly.

Identification

• Excessive mucus / slime: the fish appears coated in clear, stringy slime trails
• Peeling skin: sheets of skin or mucus visible peeling from the body, particularly the head and gill plates
• Rapid, labored breathing: gill irritation produces panting
• Loss of appetite: sudden refusal of food
• Hanging in corners or near surface: stress posture
• Color loss / paleness: stress + tissue damage
• Cloudy / pale eyes in late stages
• No white spots: the absence of visible parasites distinguishes Brooklynella from ich

How to confirm vs ich vs velvet

Visual diagnosis can be ambiguous. Quick checklist:

• White spots present? Likely ich.
• Gold-yellow dust sheen under flashlight? Likely velvet.
• Stringy mucus, peeling skin, no spots, clownfish? Likely Brooklynella.
• Rapid breathing without other symptoms? Could be any of the three; treat suspected Brooklynella aggressively given speed.

Treatment - the protocols

Protocol 1: Formalin bath (preferred)

Formaldehyde solution at therapeutic dose kills Brooklynella reliably. Two product options:

• Kordon Rid-Ich Plus (formalin + malachite green)
• Hikari Quik Cure (formalin + malachite green)
• Pure formalin (37%) diluted to therapeutic concentration - vet supply only

Protocol:

1. Set up a hospital tank: 10-20 gallon, bare bottom, sponge filter, heater, no live rock or substrate
2. Dose formalin per product label (typically 1 ml per 10 gallons for Quik Cure)
3. Cover the tank with a lid - formalin fumes are toxic to humans
4. Maintain heavy aeration - formalin reduces dissolved oxygen significantly
5. Treat for 30-45 minutes
6. Move fish to a clean QT tank (not back to display) immediately after
7. Repeat dose 24 hours later if symptoms persist
8. Continue observation in clean QT for 14 days

Critical: formalin is toxic. Wear gloves, ventilate the room, do not exceed 45 minutes of exposure for the fish. Some fish die from the treatment if dosed incorrectly.

Protocol 2: Freshwater dip (rapid intervention)

Brooklynella does not survive in fresh water. A 4-5 minute freshwater dip can knock the parasite off a fish quickly. Used as emergency intervention before formalin protocol.

1. Prepare a 1-2 gallon container of RO/DI freshwater, dechlorinated, pH-buffered to match saltwater (use Seachem Marine Buffer or similar)
2. Match temperature exactly to display tank
3. Net fish from display, place in dip container
4. Observe for 4-5 minutes - watch for distress signs (hard breathing OK; rolling or going belly-up = remove immediately)
5. Net fish, transfer to clean QT (not back to display)
6. Begin formalin protocol if not already started

Protocol 3: Chloroquine phosphate (vet-only)

Chloroquine phosphate is a research/vet drug effective against Brooklynella, ich, and velvet. Requires a veterinarian's prescription in the US. Used in extreme cases or by professional aquaculture operations.

What does NOT work

• Copper: ineffective against Brooklynella. Copper treats ich and velvet but not this parasite.
• Hyposalinity: Brooklynella tolerates lower salinity. Hyposalinity is for ich, not Brooklynella.
• UV sterilizer: kills some free-swimming stages but doesn't break the parasite cycle alone.
• "Reef-safe" disease products: almost universally useless for Brooklynella.
• Garlic in food: appetite booster only, no parasiticidal effect.

Why captive-bred clownfish dramatically reduce risk

Captive-bred clownfish from Sustainable Aquatics, ORA, Proaquatix, Bali Aquarich, and Sea & Reef are reared in controlled facilities with documented disease history. Most carry minimal-to-zero Brooklynella exposure compared to wild-caught Indonesian or Filipino imports.

If you specifically want wild-caught clownfish (some keepers prefer the bolder coloration of wild-caught Maroon or Tomato clowns), accept that prophylactic Brooklynella treatment is part of QT - even if no symptoms appear.

Prophylactic Brooklynella protocol for new wild-caught clownfish

1. Direct to QT tank (no display contact)
2. Day 1: Freshwater dip (5 min) immediately after acclimation
3. Day 2-3: Formalin bath (30-45 min)
4. Day 4-30: Observation in QT, copper protocol if intended for ich/velvet prophylaxis
5. Transfer to display only after 30 clean days

Tank-level eradication

If Brooklynella spreads to other clownfish in a display, the tank must be treated as infected:

• Remove ALL clownfish to QT immediately
• Display goes fallow for 60 days minimum (no clownfish, other fish OK)
• All clowns receive freshwater dip + formalin + observation protocol
• Tank-mates (non-clownfish) are observed for symptoms but typically not infected

The other clownfish-specific diseases

Brooklynella often co-presents with other clownfish ailments. Differential:

• Marine ich: visible white spots; treat with copper or TTM
• Marine velvet: gold dust sheen; treat with copper or hyposalinity
• Uronema: open red sores, often on body sides; treat with formalin or methylene blue
• Lymphocystis: cauliflower-like growths on fins; viral, no cure, isolate and wait it out
• Bacterial fin rot: ragged fin edges, often follows stress; treat with antibiotic (Kanaplex)

The bottom line

Brooklynella is fast, deadly, and clownfish-specific. Quarantine every new clownfish, especially wild-caught. Treat with formalin if symptoms appear. Buy captive-bred when possible to reduce risk. Speed of intervention is everything - a fish caught early survives, a fish caught late doesn't.