Introduction
Healthy fish are the heart of every thriving aquarium. Unfortunately, fish can suffer from diseases caused by parasites, bacteria, or poor water conditions. The good news? Most problems can be prevented or treated if caught early.
This guide from Aquaristic Online covers the most common fish diseases, their symptoms, causes, and effective treatments—helping you protect your aquatic pets.
White Spot Disease (Ich)
Cause: Protozoan parasite Ichthyophthirius multifiliis
Symptoms:
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White cysts on body, fins, and gills (salt-like spots)
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Rubbing against surfaces
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Labored breathing
Treatment:
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Gradually raise temperature (if species allows)
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Treat with Ich medications (copper, malachite green, or formalin)
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Increase aeration and water changes
Velvet Disease (Oodinium)
Cause: Dinoflagellate parasite Piscinoodinium
Symptoms:
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Golden dust-like sheen on skin
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Clamped fins
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Sudden lethargy, rapid gill movement
Treatment:
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Dim tank lights (parasite needs light)
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Apply copper-based anti-parasitic treatments
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Maintain pristine water quality
Columnaris (Cotton Mouth Disease)
Cause: Bacteria Flavobacterium columnare
Symptoms:
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Cottony patches on mouth, fins, or gills
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Frayed fins and ulcers
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Loss of appetite
Treatment:
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Quarantine infected fish
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Use antibiotics (kanamycin, erythromycin, oxytetracycline)
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Improve filtration and reduce waste
Dropsy
Cause: Internal bacterial infection (often water quality-related)
Symptoms:
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Severe bloating
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Pinecone-like raised scales
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Lethargy
Treatment:
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Isolate fish immediately
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Administer antibacterial food/water treatments
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Epsom salt baths for swelling
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Correct water conditions
Swim Bladder Disorder
Cause: Diet, constipation, bacterial infection, or injury
Symptoms:
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Difficulty swimming upright
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Floating/sinking abnormally
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Erratic movement
Treatment:
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Fast fish for 1–2 days
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Feed peeled, boiled peas
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Use antibacterial medication if bacterial cause suspected
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Maintain varied diet
Internal Worms and Bacteria
Cause: Parasitic worms (camallanus, nematodes, tapeworms) or gut bacteria
Symptoms:
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Stringy, red/white feces
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Weight loss despite eating
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Sunken belly
Treatment:
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Dewormers (praziquantel, flubendazole, levamisole)
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Medicated fish food
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Quarantine and substrate cleaning
Anchor Worm
Cause: External parasite Lernaea
Symptoms:
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Worm-like protrusions
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Red sores where attached
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Scratching against objects
Treatment:
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Remove parasites with sterilized tweezers
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Apply anti-parasitic meds (diflubenzuron, potassium permanganate)
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Disinfect aquarium
Flukes (Gill & Skin)
Cause: Parasitic flatworms (Gyrodactylus, Dactylogyrus)
Symptoms:
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Gasping at surface, rapid gills
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Scratching against surfaces
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Mucus on skin/gills
Treatment:
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Praziquantel-based treatments
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Quarantine affected fish
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Regular water changes
Fungal Infections
Cause: Opportunistic fungus (Saprolegnia) after injury or stress
Symptoms:
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Cotton-like white/grey growths
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Lethargy, appetite loss
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Slow healing wounds
Treatment:
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Antifungals (malachite green, methylene blue)
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Salt baths
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Improve water and reduce stress
Preventing Fish Diseases
Prevention is always better than cure. Keep fish healthy by:
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Quarantining new fish for 2 weeks
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Maintaining stable water parameters
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Feeding a varied, balanced diet
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Avoiding overcrowding
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Cleaning equipment regularly
Conclusion
Most aquarium diseases can be prevented with good care, stable water, and low stress. At Aquaristic Online, we provide premium treatments, conditioners, and fish food to keep your aquatic pets thriving.
If you suspect illness in your fish, act quickly—early treatment often makes the difference.