What are the symptoms of Fin and Tail Rot?

White or grey notches along the fin edges, spreading toward the fin base; The membrane between the fin rays dissolves first, leaving bare rays and an overall shorter fin; In severe cases the fin base turns red and bleeds, or pale cartilage is exposed; Darkened colour, clamped fins, poor appetite and resting on the bottom. It usually starts with: Elevated ammonia or nitrite continuously eroding the skin slime coat; Fin nipping and fighting creating breaks that bacteria colonise; Temperature swings, overcrowding or long gaps between water changes; Unquarantined new fish introducing pathogenic bacteria to a tank with existing wounds.

How do you treat Fin and Tail Rot?

In order: 1. Test the water, then change it (This is the first step, not an optional one: test ammonia, nitrite and nitrate, then change 30-50% of the water with matched temperature and clean the substrate. Most fin rot is a water problem, and fins often start regrowing once water is fixed.) 2. Isolate severely affected fish (Move fish with red fin bases or extensive loss into a hospital tank for medication; mild cases can stay in the display tank and recover through better water and reduced density.) 3. Change water daily or every other day (During treatment change 20-30% of the water every one to two days with matched temperature, keeping ammonia and nitrite undetectable - that is the precondition for regrowth.) 4. Short salt bath (Use 1-3 g of non-iodised salt per litre in the hospital tank for 5-7 days. Skip salt for scaleless fish such as loaches, plecos and corydoras, and rely on water changes and antibiotics instead.) 5. Antibiotics if water quality alone fails (If the rot keeps advancing after 3-5 days, use an antibacterial in the hospital tank (oxytetracycline, florfenicol or similar, per the label) and finish the whole course without stopping early.) 6. Look for the new translucent fin margin (The sign of recovery is a translucent new margin appearing along the fin edge; full regrowth takes weeks to months, and stable water is all it needs.)

What medication treats Fin and Tail Rot?

Oxytetracycline: Hospital tank only, as a bath or in food at the label dose for about 5-7 days. Antibiotics kill nitrifying bacteria, so dosing the display tank easily causes an ammonia rebound; switch off UV and remove carbon during treatment.; Florfenicol: Hospital tank only, mixed into food at the label dose for 5-10 days. It is a prescription-class antibacterial, so check local regulations and withdrawal periods.; Furan-based antibacterials: Hospital tank only, as a bath at the label dose for 5-7 days. They affect the biofilter and invertebrates, so change water and run activated carbon afterwards.

G-04 / 06Freshwater

Fin and Tail Rot烂鳍烂尾病

Moderate. Caught early it reverses with better water alone; waiting until the fin base reddens and bleeds usually leaves permanent damage.

Illustration to come

G-04 / 06 · Fin and Tail Rot

SpecificationsDisease atlas

Cause: Bacteria
Severity: Moderate
Contagion: Highly contagious
Corals / inverts: Not safe
Also known as: Tail rot、Bacterial fin rot

Symptoms

White or grey notches along the fin edges, spreading toward the fin base
The membrane between the fin rays dissolves first, leaving bare rays and an overall shorter fin
In severe cases the fin base turns red and bleeds, or pale cartilage is exposed
Darkened colour, clamped fins, poor appetite and resting on the bottom

Typical triggers

— Elevated ammonia or nitrite continuously eroding the skin slime coat
— Fin nipping and fighting creating breaks that bacteria colonise
— Temperature swings, overcrowding or long gaps between water changes
— Unquarantined new fish introducing pathogenic bacteria to a tank with existing wounds

Treatment, in order

1 · Water changeTest the water, then change itThis is the first step, not an optional one: test ammonia, nitrite and nitrate, then change 30-50% of the water with matched temperature and clean the substrate. Most fin rot is a water problem, and fins often start regrowing once water is fixed.
2 · IsolateIsolate severely affected fishMove fish with red fin bases or extensive loss into a hospital tank for medication; mild cases can stay in the display tank and recover through better water and reduced density.
3 · Water changeChange water daily or every other dayDuring treatment change 20-30% of the water every one to two days with matched temperature, keeping ammonia and nitrite undetectable - that is the precondition for regrowth.
4 · SaltShort salt bathUse 1-3 g of non-iodised salt per litre in the hospital tank for 5-7 days. Skip salt for scaleless fish such as loaches, plecos and corydoras, and rely on water changes and antibiotics instead.
5 · MedicationAntibiotics if water quality alone failsIf the rot keeps advancing after 3-5 days, use an antibacterial in the hospital tank (oxytetracycline, florfenicol or similar, per the label) and finish the whole course without stopping early.
6 · ObserveLook for the new translucent fin marginThe sign of recovery is a translucent new margin appearing along the fin edge; full regrowth takes weeks to months, and stable water is all it needs.

The standard treatment uses copper or formalin, which is lethal to corals, shrimp, snails and everything on live rock. Treat in a quarantine tank only, and leave the display tank fallow for the full period above before returning the fish.

Medications and cautions

Oxytetracycline: Hospital tank only, as a bath or in food at the label dose for about 5-7 days. Antibiotics kill nitrifying bacteria, so dosing the display tank easily causes an ammonia rebound; switch off UV and remove carbon during treatment.
Florfenicol: Hospital tank only, mixed into food at the label dose for 5-10 days. It is a prescription-class antibacterial, so check local regulations and withdrawal periods.
Furan-based antibacterials: Hospital tank only, as a bath at the label dose for 5-7 days. They affect the biofilter and invertebrates, so change water and run activated carbon afterwards.

Prevention

Keep ammonia and nitrite undetectable with regular water changes
Avoid mixing aggressive fish with long-finned species and provide plenty of cover
Quarantine new fish for 2-4 weeks before adding them
Hold the temperature gap within 1 °C at water changes

Frequently asked questions

What are the symptoms of Fin and Tail Rot?: White or grey notches along the fin edges, spreading toward the fin base; The membrane between the fin rays dissolves first, leaving bare rays and an overall shorter fin; In severe cases the fin base turns red and bleeds, or pale cartilage is exposed; Darkened colour, clamped fins, poor appetite and resting on the bottom. It usually starts with: Elevated ammonia or nitrite continuously eroding the skin slime coat; Fin nipping and fighting creating breaks that bacteria colonise; Temperature swings, overcrowding or long gaps between water changes; Unquarantined new fish introducing pathogenic bacteria to a tank with existing wounds.
How do you treat Fin and Tail Rot?: In order: 1. Test the water, then change it (This is the first step, not an optional one: test ammonia, nitrite and nitrate, then change 30-50% of the water with matched temperature and clean the substrate. Most fin rot is a water problem, and fins often start regrowing once water is fixed.) 2. Isolate severely affected fish (Move fish with red fin bases or extensive loss into a hospital tank for medication; mild cases can stay in the display tank and recover through better water and reduced density.) 3. Change water daily or every other day (During treatment change 20-30% of the water every one to two days with matched temperature, keeping ammonia and nitrite undetectable - that is the precondition for regrowth.) 4. Short salt bath (Use 1-3 g of non-iodised salt per litre in the hospital tank for 5-7 days. Skip salt for scaleless fish such as loaches, plecos and corydoras, and rely on water changes and antibiotics instead.) 5. Antibiotics if water quality alone fails (If the rot keeps advancing after 3-5 days, use an antibacterial in the hospital tank (oxytetracycline, florfenicol or similar, per the label) and finish the whole course without stopping early.) 6. Look for the new translucent fin margin (The sign of recovery is a translucent new margin appearing along the fin edge; full regrowth takes weeks to months, and stable water is all it needs.)
Is Fin and Tail Rot contagious, and how urgent is it?: Contagion: highly contagious. Severity: moderate. Cause: bacteria. Moderate. Caught early it reverses with better water alone; waiting until the fin base reddens and bleeds usually leaves permanent damage.
What medication treats Fin and Tail Rot?: Oxytetracycline: Hospital tank only, as a bath or in food at the label dose for about 5-7 days. Antibiotics kill nitrifying bacteria, so dosing the display tank easily causes an ammonia rebound; switch off UV and remove carbon during treatment.; Florfenicol: Hospital tank only, mixed into food at the label dose for 5-10 days. It is a prescription-class antibacterial, so check local regulations and withdrawal periods.; Furan-based antibacterials: Hospital tank only, as a bath at the label dose for 5-7 days. They affect the biofilter and invertebrates, so change water and run activated carbon afterwards.
Is the treatment for Fin and Tail Rot safe for corals and inverts?: No. The standard treatment (copper or formalin based) is lethal to corals, shrimp, snails and everything on live rock. Treat in a quarantine tank only, and leave the display tank fallow for the full period given above.