Fish disease library

Browse every disease, parasite, and bacterial infection covered in our knowledge base. Pick filters to narrow it down — results update as you go.

43 conditions

Freshwater Tropical

Columnaris

A highly contagious bacterial infection (Flavobacterium columnare) presenting as white/grey patches, often on the mouth, fins, or gills.…

Severe

Freshwater Tropical

Aeromonas (Ulcer Disease)

Bacterial infection causing open ulcers, hemorrhagic patches, and red sores. The #1 cause of mortality in koi ponds…

Critical

Freshwater Tropical

Mycobacteriosis (Fish Tuberculosis)

A slow, chronic infection caused by Mycobacterium spp. Symptoms include emaciation, spinal deformity, and granulomas. Zoonotic risk —…

Critical

Freshwater Tropical

Hexamita (Hole-in-the-Head)

Intestinal flagellate parasite causing pitted lesions on the head and lateral line, especially in cichlids and discus. Often…

Moderate

Freshwater Tropical

Fin Rot

Progressive deterioration of fin tissue caused by opportunistic bacteria — usually a symptom of poor water quality.

Mild

Freshwater Tropical

Velvet (Oodinium)

Dinoflagellate parasite producing a fine, gold-dust coating across the body. More lethal than ich; gill infection causes rapid…

Severe

Freshwater Tropical

Dropsy

Bloated body with pinecone-stuck-out scales — a symptom of organ failure, not a disease itself. Prognosis is generally…

Critical

Freshwater Tropical

Swim Bladder Disorder

Loss of buoyancy control — fish floats, sinks, or swims at odd angles. Common in fancy goldfish and…

Moderate

Freshwater Tropical

Cloudy Eye

Hazy or opaque film over one or both eyes — usually a sign of bacterial infection or chronic…

Moderate

Freshwater Tropical

Branchiomycosis (Gill Rot)

Fungus (true fungus) disease of aquarium fish. Key signs: rapid breathing, gasping at surface, gill necrosis with white/marbled…

Severe

Freshwater Tropical

Lymphocystis Disease

Virus disease of aquarium fish. Key signs: wart-like, cauliflower-shaped, pinkish-white nodules on skin and fins (greatly enlarged virus-infected…

Mild

Freshwater Tropical

Streptococcosis

Bacterium disease of aquarium fish. Key signs: exophthalmia (often unilateral, 'pop-eye'), corneal opacity, spinning/spiral swimming, darkening, hemorrhages around…

Severe

Freshwater Tropical

Costia (Ichthyobodo)

Parasite (flagellated protozoan) disease of aquarium fish. Key signs: blue-grey film of mucus over skin ('slime disease'), peeling…

Moderate

Freshwater Tropical

Trichodina Infestation

Parasite (ciliate protozoan) disease of aquarium fish. Key signs: excessive mucus (slime coat), pale or 'milky' patches on…

Moderate

Freshwater Tropical

Fish Lice (Argulus)

Parasite (branchiuran crustacean) disease of aquarium fish. Key signs: flat, round, 5–10 mm semi-transparent lice visible attached to…

Moderate

Freshwater Tropical

Hole-in-the-Head Disease (Hexamita)

Parasite (flagellated protozoan) disease of aquarium fish. Key signs: pinhole-sized pits on head that enlarge into cavities; lesions…

Moderate

Freshwater Tropical

Fin and Tail Rot

Bacterium (mixed/opportunistic) disease of aquarium fish. Key signs: ragged, frayed or eroded fin edges; white margins followed by…

Moderate

Freshwater Tropical

Saprolegnia (Cotton Mold)

Oomycete disease of aquarium fish. Key signs: cotton-wool-like white or grey patches on skin, fins or eggs, often…

Moderate

Freshwater Tropical

Ich (White Spot Disease)

Parasite (ciliate protozoan) disease of aquarium fish. Key signs: small pinhead-sized white spots (cysts) on skin and fins;…

Moderate

Freshwater Tropical

Ceratomyxosis

Parasite (myxosporean) disease of aquarium fish. Key signs: distended abdomen, ascites, hemorrhagic enteritis, lethargy, blackened tail, anaemia; chronic…

Critical