Disease Intelligence Center
What's Wrong With Your Fish?
Search symptoms, diseases, or treatments to identify problems quickly.
Priority 1
Emergency Conditions
High-risk conditions to check first when fish are gasping, collapsing, or dying fast.
Columnaris
Emergency
A lethal gram-negative bacterial infection that mimics fungus and kills fish within 48 hours without prompt antibiotics.
Water Quality
Contagious: Direct contact, waterborne
Freshwater
Immediate
A lethal gram-negative bacterial infection that mimics fungus and kills fish within 48 hours without prompt antibiotics.
Dropsy
Emergency
A critical fluid-retention syndrome causing pinecone scales from bacterial kidney infection.
Water Quality
Contagious: Internal, opportunistic
Freshwater
Immediate
pineconing
Ich (White Spot Disease)
Emergency
A highly contagious protozoan parasite producing white salt-grain spots that can kill entire tank populations without prompt treatment.
Water Quality
Contagious: Direct contact, waterborne
Freshwater
Immediate
A highly contagious protozoan parasite producing white salt-grain spots that can kill entire tank populations without prompt treatment.
Velvet (Gold Dust Disease)
Emergency
A highly lethal, microscopic parasite that coats the fish in a fine, rust-colored or gold dust-like film, causing severe respiratory distress.
Water Quality
Contagious: Direct contact, free-swimming dinospores, contaminated equipment
Freshwater
Immediate
A highly lethal, microscopic parasite that coats the fish in a fine, rust-colored or gold dust-like film, causing severe respiratory distress.
Primary navigation
Diagnose by Symptoms
Use symptoms first, not disease names. Selecting a symptom filters the disease list below.
Most common
Common Diseases
Compact editorial cards with severity, water type, contagious status, and top symptoms.
Fin Rot
High
A progressive bacterial infection that frays and destroys fin tissue, typically triggered by poor water quality.
Bacterial
Contagious: Environmental, opportunistic
Freshwater
3-10 days
frayed fins
Dropsy
Emergency
A critical fluid-retention syndrome causing pinecone scales from bacterial kidney infection.
Water Quality
Contagious: Internal, opportunistic
Freshwater
24-72 hours
pineconing
Swim Bladder Disease
High
A buoyancy disorder causing fish to float upside down, sink, or struggle to swim upright, often linked to overfeeding or genetics.
Water Quality
Contagious: Non-contagious
Freshwater
3-10 days
swimming upside down
Browse
Disease Categories
All
Parasites
Bacterial
Fungal
Viral
Water Quality
Nutritional
Environmental
Genetic
Action
Diagnostic Tools
Bridge disease identification with the calculators people need right away.
Calculator
Ammonia Toxicity Calculator (Free NH3)
Enter your test kit reading (TAN), pH, and temperature — get an instant SAFE or LETHAL verdict for Free Ammonia (NH3). Built for API Master Kit users, cichlid tanks, reef setups, and fish breeders.
Calculator
Nitrite Toxicity Risk Calculator
Nitrite poisoning — known as Brown Blood Disease — can silently suffocate your fish even in a crystal-clear, well-oxygenated tank. This calculator factors in your actual pH and water temperature to show you exactly how toxic your nitrite reading is right now, and what you need to do about it.
Calculator
Aquarium Water Changes Calculator
Calculate safer water change percentages for nitrate reduction, emergency dilution, routine maintenance, and stable aquarium water quality. Enter your tank volume, current and target levels — get exact gallons, serial change plans, and safety warnings for sensitive species.
Calculator
Aquarium Medication Dosage Calculator
Enter your tank size, substrate displacement, and medication type — get an exact safe dose based on true net water volume. Includes scaleless fish half-dose warnings for copper, formalin, and malachite green treatments.
Calculator
Fish Compatibility Calculator
Use the Coexistence Lab to cross-reference temperaments, temperature bounds, pH ranges, and swimming depths of freshwater species before adding them to your aquarium. Prevent territorial disputes, physical injury, and chemical shock before you buy.
Treatment journey
From Diagnosis to Recovery
1
Identify
2
Confirm Water Quality
3
Treat
4
Monitor Recovery
5
Prevent Future Disease
Prevention & learning
Prevention & Learning
Keep disease from coming back with quarantine, water quality, and prevention guides.
Directory
Complete Disease Directory
Anchor Worm / Fish Lice
High
Visible crustacean parasites that embed in koi and goldfish skin, causing ulcerative wounds.
Water Quality
Contagious: Direct contact, infected plants/water
Freshwater
3-10 days
Visible crustacean parasites that embed in koi and goldfish skin, causing ulcerative wounds.
Columnaris
Emergency
A lethal gram-negative bacterial infection that mimics fungus and kills fish within 48 hours without prompt antibiotics.
Water Quality
Contagious: Direct contact, waterborne
Freshwater
24-72 hours
A lethal gram-negative bacterial infection that mimics fungus and kills fish within 48 hours without prompt antibiotics.
Dropsy
Emergency
A critical fluid-retention syndrome causing pinecone scales from bacterial kidney infection.
Water Quality
Contagious: Internal, opportunistic
Freshwater
24-72 hours
pineconing
Fin Rot
High
A progressive bacterial infection that frays and destroys fin tissue, typically triggered by poor water quality.
Bacterial
Contagious: Environmental, opportunistic
Freshwater
3-10 days
frayed fins
Flukes
High
Microscopic flatworm parasites that infest gills and skin, causing severe itching, flashing, and respiratory distress.
Water Quality
Contagious: Direct contact, free-swimming larvae
Freshwater
3-10 days
Microscopic flatworm parasites that infest gills and skin, causing severe itching, flashing, and respiratory distress.
Hemorrhagic Septicemia
High
A lethal bacterial bloodstream infection causing red streaks, hemorrhaging, and organ failure in stressed fish.
Water Quality
Contagious: Internal, waterborne
Freshwater
3-10 days
A lethal bacterial bloodstream infection causing red streaks, hemorrhaging, and organ failure in stressed fish.
Hexamita / Hole-in-the-Head
High
A parasitic infection causing facial pitting and lateral line erosion in cichlids, driven by poor water quality and nutritional deficiency.
Water Quality
Contagious: Internal, opportunistic
Freshwater
3-10 days
A parasitic infection causing facial pitting and lateral line erosion in cichlids, driven by poor water quality and nutritional deficiency.
Ich (White Spot Disease)
Emergency
A highly contagious protozoan parasite producing white salt-grain spots that can kill entire tank populations without prompt treatment.
Water Quality
Contagious: Direct contact, waterborne
Freshwater
24-72 hours
A highly contagious protozoan parasite producing white salt-grain spots that can kill entire tank populations without prompt treatment.
Internal Parasites / Worms
High
A parasitic infection of the digestive tract causing wasting, stringy feces, and malabsorption in aquarium fish.
Water Quality
Contagious: Ingestion of cysts, wild-caught fish
Freshwater
3-10 days
A parasitic infection of the digestive tract causing wasting, stringy feces, and malabsorption in aquarium fish.
Swim Bladder Disease
High
A buoyancy disorder causing fish to float upside down, sink, or struggle to swim upright, often linked to overfeeding or genetics.
Water Quality
Contagious: Non-contagious
Freshwater
3-10 days
swimming upside down
True Fungus
High
An opportunistic oomycete infection producing fluffy cotton-wool growths on dead or damaged fish tissue.
Water Quality
Contagious: Opportunistic on dead tissue
Freshwater
3-10 days
An opportunistic oomycete infection producing fluffy cotton-wool growths on dead or damaged fish tissue.
Velvet (Gold Dust Disease)
Emergency
A highly lethal, microscopic parasite that coats the fish in a fine, rust-colored or gold dust-like film, causing severe respiratory distress.
Water Quality
Contagious: Direct contact, free-swimming dinospores, contaminated equipment
Freshwater
24-72 hours
A highly lethal, microscopic parasite that coats the fish in a fine, rust-colored or gold dust-like film, causing severe respiratory distress.