Common Aquarium Fish Diseases: Symptoms, Causes & Treatment

Even in well-maintained aquariums, fish can get sick. The key to successful treatment is early identification and prompt action. This comprehensive guide covers the most common aquarium fish diseases, their symptoms, causes, and treatments.

Prevention: The Best Medicine

Before diving into diseases, remember that prevention is always better than cure:

• Quarantine new fish for 2-4 weeks before adding to main tank
• Maintain water quality with regular testing and water changes
• Don't overstock your aquarium
• Feed a varied, quality diet
• Avoid sudden temperature or pH changes
• Remove sick fish promptly to hospital tank

Ich (White Spot Disease)

Also known as: Ick, Ichthyophthirius multifiliis

Symptoms

• White spots resembling salt grains on body and fins
• Scratching against objects (flashing)
• Clamped fins
• Lethargy
• Loss of appetite
• Rapid gill movement

Cause

A parasitic protozoan with a complex life cycle. Often triggered by stress, temperature drops, or new fish introduction.

Treatment

Step 1: Raise temperature to 82-86°F (gradually, 1-2 degrees per day)

• Higher temperatures speed up the parasite life cycle, making treatment more effective

Step 2: Add aquarium salt (1 tablespoon per 5 gallons)

• Helps fish cope with osmotic stress

Step 3: Medicate

• Ich-X (Hikari) - safe for scaleless fish
• Super Ick Cure (API)
• Paraguard (Seachem)

Step 4: Continue treatment for 3-5 days after last spot disappears

Important Notes

• Ich is only vulnerable to medication during its free-swimming stage
• The entire tank must be treated, not just affected fish
• Remove carbon from filter during treatment

Fin Rot

Symptoms

• Ragged, frayed, or eroding fins
• White edges on fin damage
• Red streaks in fins (in severe cases)
• Fins may look "melted"
• Secondary fungal infection possible

Cause

Bacterial infection (usually Pseudomonas, Aeromonas, or Vibrio), almost always secondary to poor water quality, stress, or injury.

Treatment

Mild Cases:

1. Improve water quality immediately (50% water change)
2. Add aquarium salt (1 tsp per gallon)
3. Keep water pristine - daily partial water changes
4. Often resolves without medication

Severe Cases:

1. Move to hospital tank
2. Treat with antibiotics:

- Kanaplex (Seachem) - gram-negative bacteria

- API Fin & Body Cure

- Maracyn (Fritz)

1. Keep water warm and clean

Prevention

• Maintain excellent water quality
• Avoid aggressive tankmates that may nip fins
• Don't overcrowd

Dropsy

Symptoms

• Severely bloated body
• Scales sticking out like a pinecone (pathognomonic sign)
• Bulging eyes (sometimes)
• Lethargy
• Loss of appetite
• Pale feces

Cause

Not a disease itself but a symptom of organ failure, usually kidney. Often caused by bacterial infection, though parasites, cancer, and old age can contribute.

Treatment

Prognosis: Unfortunately often poor. By the time scales are raised, significant internal damage has occurred.

Attempt:

1. Isolate in hospital tank
2. Epsom salt bath (1 tbsp per gallon) - helps reduce fluid
3. Antibiotic treatment:

- Kanaplex

- Maracyn 2

1. Feed medicated food if fish is eating

When to Consider Euthanasia

If the fish shows no improvement after 7-10 days of treatment and is clearly suffering, humane euthanasia may be the kindest option.

Velvet Disease

Symptoms

• Gold or rust-colored "dust" on body (visible at angle with flashlight)
• Scratching against objects
• Clamped fins
• Rapid gill movement
• Lethargy

Cause

Parasitic dinoflagellate (Piscinoodinium/Oodinium). Spreads extremely fast and can wipe out a tank quickly.

Treatment

1. Dim lights - the parasite uses photosynthesis
2. Raise temperature to 80-82°F
3. Medicate immediately:

- Copper-based treatment (most effective)

- Ich-X

- Paraguard

1. Treat for 10-14 days minimum

Warning

Velvet is highly contagious and more deadly than ich. Act fast!

Columnaris (Cotton Mouth Disease)

Symptoms

• White or gray patches resembling cotton or fungus
• Usually starts at mouth, gills, or wounds
• Frayed fins
• Rapid progression
• Fish may gasp at surface

Cause

Bacterial (Flavobacterium columnare). Often confused with fungus but requires different treatment.

Treatment

1. Lower temperature to 75°F (slows bacterial growth)
2. Treat with antibiotics:

- Kanaplex + Furan 2 (combination most effective)

- API Triple Sulfa

1. Add salt (1 tsp per gallon)
2. Improve water quality

Note

Columnaris thrives in warm water - opposite of ich treatment!

Fungal Infections

Symptoms

• Cotton-like white growths
• Usually develops on wounds or damaged areas
• May have a "hairy" appearance
• Often secondary to bacterial infections

Cause

Various fungal species (Saprolegnia most common). Usually opportunistic infection on already damaged tissue.

Treatment

1. Identify and treat underlying cause (injury, bacterial infection)
2. Anti-fungal medication:

- Pimafix

- Methylene blue

- API Fungus Cure

1. Salt baths (1 tbsp per gallon for 30 min)
2. Maintain clean water

Swim Bladder Disease

Symptoms

• Fish floats uncontrollably
• Fish sinks and can't rise
• Fish swims sideways or upside down
• Bloated belly (sometimes)

Causes

• Constipation (most common)
• Bacterial infection
• Physical injury
• Genetic deformity

Treatment

For constipation:

1. Fast the fish for 3 days
2. Feed deshelled pea (blanched)
3. Raise temperature to 78-80°F
4. Add Epsom salt (1 tbsp per 5 gallons)

For infection:

1. Antibiotic treatment
2. Hospital tank

For genetic/permanent damage:

Some fish adapt and live normal lives; others may need to be euthanized if quality of life is poor.

Anchor Worms

Symptoms

• Visible worm-like parasites attached to body
• Red, irritated attachment site
• Fish scratching
• Ulcers at attachment points

Cause

Parasitic crustacean (Lernaea). Often introduced on new fish or plants.

Treatment

1. Manually remove visible worms with tweezers
2. Treat wound with iodine or hydrogen peroxide
3. Treat entire tank:

- Dimilin

- Cyromazine

- Salt dips (30 ppt for 5-10 min)

1. Repeat treatment in 2 weeks (catch hatching eggs)

Setting Up a Hospital Tank

Every fishkeeper should have a hospital tank ready:

Basic setup:

• 10-20 gallon tank (depending on fish size)
• Sponge filter (established or with media from main tank)
• Heater
• Thermometer
• Simple hiding spot (PVC pipe works)
• NO substrate (easier to keep clean)
• NO plants (medication may harm them)

Benefits:

• Isolates sick fish to prevent spread
• Allows targeted medication without treating whole tank
• Easier to observe sick fish
• More cost-effective (less medication needed)

Medication Safety

General rules:

• Remove activated carbon during treatment
• Maintain aeration (some meds reduce oxygen)
• Follow dosage instructions exactly
• Complete full treatment course
• Don't mix medications without research
• Store medications properly

Scaleless fish caution:

Loaches, catfish, and other scaleless fish are sensitive to many medications. Always use half dose or choose scaleless-safe alternatives.

When to Euthanize

Sometimes, despite our best efforts, a fish cannot be saved. Humane euthanasia is appropriate when:

• The fish has stopped eating for an extended period
• There's no response to treatment
• The fish is clearly suffering
• Disease is terminal (advanced dropsy, tumors)

Humane methods:

• Clove oil overdose (most recommended)
• Rapid freezing is NOT humane (ice crystals cause suffering)

Conclusion

Knowing how to identify and treat fish diseases is an essential skill for any aquarist. The most important factors for success are:

1. Early detection - observe your fish daily
2. Prompt action - don't wait to see if it gets worse
3. Proper diagnosis - wrong treatment can make things worse
4. Complete treatment - don't stop early even if fish looks better
5. Prevention - maintain excellent water quality

Keep this guide bookmarked and a hospital tank ready. Your fish are counting on you!