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Fish Health Reference

Fish Diseases Database

Comprehensive pathogen, symptom, diagnosis and treatment guides for viral, bacterial, parasitic and fungal fish diseases — used by aquaculturists, veterinarians and hobbyists.

🦠 80 diseases 🔔 15 OIE notifiable 💉 16 with vaccine
Severity:
Henneguya Salminicola Infection
Parasitic ⚪ Sublethal
🦠 Henneguya salminicola

A myxozoan tissue parasite of Pacific salmon muscle causing grossly visible white milky cysts, rende...

Ligula Intestinalis Infection
Parasitic ⚪ Sublethal
🦠 Ligula intestinalis

A plerocercoid cestode (tapeworm) infection of freshwater fish, in which the large ribbon-like larva...

Red Mark Syndrome
RMS Bacterial ⚪ Sublethal
🦠 Candidatus Clavichlamydia salmonicola (suspected)

A poorly understood skin condition of farmed Atlantic salmon characterised by irregular red marks on...

Ammonia Toxicity
Environmental 🔴 Fatal
🦠 Total ammonia nitrogen (TAN); unionised NH₃ is the toxic form

Toxic accumulation of unionised ammonia (NH₃) in fish water causing gill damage, neurological dysfun...

Amoebic Gill Disease
AGD Parasitic 🔴 Fatal
🦠 Neoparamoeba perurans

A severe parasitic gill disease of sea-water Atlantic salmon caused by the marine amoeba Neoparamoeb...

Full guide ✓ Treatable
Aphanomyces Invadans (MAS Ulcerative Disease)
EUS Fungal 🔴 Fatal 🔔 Notifiable
🦠 Aphanomyces invadans (syn. A. piscicida)

A necrotising oomycete disease of freshwater and estuarine fish caused by Aphanomyces invadans, prod...

Bacterial Kidney Disease
BKD Bacterial 🔴 Fatal
🦠 Renibacterium salmoninarum

A chronic systemic bacterial disease of salmonids caused by Renibacterium salmoninarum, primarily af...

Ceratomyxosis
Parasitic 🔴 Fatal
🦠 Ceratomyxa shasta

A lethal myxozoan gut disease of Pacific salmonids in the Columbia River basin caused by Ceratomyxa...

Channel Catfish Virus Disease
CCVD Viral 🔴 Fatal 🔔 Notifiable
🦠 Channel catfish virus (CCV / Ictalurid herpesvirus 1)

A highly lethal herpesviral disease of juvenile channel catfish caused by Ictalurid herpesvirus 1, c...

Chilodonella Infection
Parasitic 🔴 Fatal
🦠 Chilodonella uncinata, C. hexasticha

A parasitic ciliate infection of the skin and gills of freshwater fish caused by Chilodonella spp.,...

Full guide ✓ Treatable
Copper Toxicity
Environmental 🔴 Fatal
🦠 Dissolved copper (Cu²⁺) in water

Toxic accumulation of dissolved copper ions in water, causing gill damage, mucus hyperproduction, ne...

Cryptobiosis (Cryptobia salmositica)
Parasitic 🔴 Fatal
🦠 Cryptobia salmositica

A haemoflagellate blood parasite disease of Pacific salmonids caused by Cryptobia salmositica, trans...

Cyprinid Herpesvirus 2 Disease
CyHV-2 Viral 🔴 Fatal
🦠 Cyprinid herpesvirus 2 (CyHV-2)

A herpesviral disease of goldfish and crucian carp causing severe haematopoietic necrosis, gill dama...

Enteric Septicaemia of Catfish
ESC Bacterial 🔴 Fatal
🦠 Edwardsiella ictaluri

The most economically important disease of the US channel catfish aquaculture industry, causing ente...

Full guide ✓ Treatable
Epizootic Haematopoietic Necrosis
EHN Viral 🔴 Fatal 🔔 Notifiable
🦠 Epizootic haematopoietic necrosis virus (EHNV)

A severe iridoviral disease endemic to Australia, causing massive necrosis of haematopoietic tissues...

Exophiala Fungal Infection
Fungal 🔴 Fatal
🦠 Exophiala angulospora, E. pisciphila, E. salmonis

A systemic fungal infection of fish caused by black yeast-like fungi of the genus Exophiala, causing...

Flavobacterium psychrophilum Infection
RTFS/BCWD Bacterial 🔴 Fatal
🦠 Flavobacterium psychrophilum

Rainbow Trout Fry Syndrome (RTFS) and Bacterial Cold Water Disease (BCWD) in salmon — two manifestat...

Full guide ✓ Treatable
Furunculosis
Bacterial 🔴 Fatal
🦠 Aeromonas salmonicida subsp. salmonicida

A systemic bacterial disease of salmonids caused by Aeromonas salmonicida, characterised by boil-lik...

Full guide ✓ Treatable
Gas Bubble Disease
GBD Environmental 🔴 Fatal
🦠 Supersaturation of dissolved gases (primarily nitrogen and/or oxygen)

Emboli (bubbles) forming in fish tissue and blood when dissolved gas supersaturation (>110% total di...

Gyrodactylus salaris (Monogenean Fluke)
Parasitic 🔴 Fatal 🔔 Notifiable
🦠 Gyrodactylus salaris

A monogenean ectoparasite devastating to naive Atlantic Salmon populations, causing hyperinfection a...

Full guide ✓ Treatable
Ichthyobodo (Costia) Infection
Parasitic 🔴 Fatal
🦠 Ichthyobodo necator (formerly Costia necatrix)

A protozoan ectoparasite infection caused by the flagellate Ichthyobodo necator, attaching to skin a...

Full guide ✓ Treatable
Ichthyophthirius multifiliis (White Spot)
Ich Parasitic 🔴 Fatal
🦠 Ichthyophthirius multifiliis

The most common and devastating freshwater fish disease globally — caused by the holotrophic ciliate...

Full guide ✓ Treatable
Infectious Haematopoietic Necrosis
IHN Viral 🔴 Fatal 🔔 Notifiable
🦠 Infectious haematopoietic necrosis virus (IHNV)

A rhabdoviral disease causing haematopoietic (blood-forming tissue) necrosis in salmonids, particula...

Full guide 💉 Vaccine
Infectious Salmon Anaemia
ISA Viral 🔴 Fatal 🔔 Notifiable
🦠 Infectious salmon anaemia virus (ISAV)

A severe viral disease of Atlantic Salmon caused by ISAV, characterised by high mortality in sea-wat...

Full guide 💉 Vaccine
Koi Herpesvirus Disease
KHV/KHVD Viral 🔴 Fatal 🔔 Notifiable
🦠 Cyprinid herpesvirus 3 (CyHV-3)

A highly contagious and lethal herpesviral disease of koi and common carp, causing mass mortality at...

Full guide 💉 Vaccine
Lactococcosis
Bacterial 🔴 Fatal
🦠 Lactococcus garvieae

A gram-positive bacterial septicaemia of fish caused by Lactococcus garvieae, causing haemorrhagic s...

Full guide ✓ Treatable
M74 Syndrome (Thiamine Deficiency)
M74 Environmental 🔴 Fatal
🦠 Thiamine (Vitamin B1) deficiency in maternal diet

A nutritional disorder in salmonid offspring caused by maternal thiamine (Vitamin B1) deficiency, re...

Full guide ✓ Treatable
Mycobacteriosis (Fish Tuberculosis)
Bacterial 🔴 Fatal
🦠 Mycobacterium marinum, M. fortuitum, M. chelonae

A chronic granulomatous disease of fish caused by acid-fast mycobacteria, forming granulomas through...

Nitrite Toxicity (Brown Blood Disease)
Environmental 🔴 Fatal
🦠 Nitrite (NO₂⁻) oxidises haemoglobin to methaemoglobin

Poisoning by elevated nitrite in water, which enters fish gills and oxidises haemoglobin to methaemo...

Oodinium (Velvet Disease)
Parasitic 🔴 Fatal
🦠 Amyloodinium ocellatum (marine), Piscinoodinium pillulare (freshwater)

A dinoflagellate ectoparasitic disease causing a characteristic golden-yellow "velvet" or "rust" dus...

Full guide ✓ Treatable
Oxygen Depletion Stress
Environmental 🔴 Fatal
🦠 Dissolved oxygen <4 mg/L (hypoxia) or <2 mg/L (severe hypoxia)

Mass mortality or sublethal physiological stress in fish caused by insufficient dissolved oxygen in...

Pasteurellosis
Bacterial 🔴 Fatal
🦠 Photobacterium damselae subsp. piscicida

An acute or subacute bacterial septicaemia of marine fish caused by Photobacterium damselae subsp. p...

Full guide ✓ Treatable
pH Acidosis / Acid Stress
Environmental 🔴 Fatal
🦠 Water pH <6.0 (acute toxicity); pH <7.0 chronic stress in sensitive species

Physiological damage or death in fish caused by exposure to acidic water (low pH), impairing ion reg...

Piscirickettsiosis
SRS Bacterial 🔴 Fatal 🔔 Notifiable
🦠 Piscirickettsia salmonis

A salmonellosis-like rickettsial disease of salmonids caused by the obligate intracellular bacterium...

Full guide 💉 Vaccine
Red Sea Bream Iridoviral Disease
RSIVD Viral 🔴 Fatal 🔔 Notifiable
🦠 Red sea bream iridovirus (RSIV)

A severe iridoviral disease of marine fish caused by Red Sea Bream Iridovirus, a Megalocytivirus cha...

Full guide 💉 Vaccine
Saprolegniasis (Water Mould)
Fungal 🔴 Fatal
🦠 Saprolegnia parasitica, S. diclina

A water mould (oomycete) infection producing characteristic white-grey cotton-wool tufts on the skin...

Spring Viraemia of Carp
SVC Viral 🔴 Fatal 🔔 Notifiable
🦠 Spring viraemia of carp virus (SVCV)

A rhabdoviral haemorrhagic disease of cyprinids occurring primarily in spring when water temperature...

Tilapia Lake Virus
TiLV Viral 🔴 Fatal 🔔 Notifiable
🦠 Tilapia tilapinevirus

An emerging viral disease of tilapia causing syncytial encephalitis and high mortality, spreading ra...

Ulcerative Dermal Necrosis
UDN Viral 🔴 Fatal
🦠 Unknown (suspected viral; Herpesvirus salmonis implicated)

A mysterious ulcerative skin disease of adult returning Atlantic Salmon in UK and Irish rivers, prod...

Vibriosis
Bacterial 🔴 Fatal
🦠 Vibrio anguillarum (syn. Listonella anguillarum)

A haemorrhagic septicaemia of marine and estuarine fish caused by Vibrio anguillarum, producing exte...

Full guide ✓ Treatable
Viral Haemorrhagic Septicaemia
VHS Viral 🔴 Fatal 🔔 Notifiable
🦠 Viral haemorrhagic septicaemia virus (VHSV)

A rhabdoviral haemorrhagic disease of great epidemiological importance affecting a wide range of mar...

Viral Nervous Necrosis
VNN/VER Viral 🔴 Fatal
🦠 Betanodavirus (nervous necrosis virus, NNV)

A nodaviral disease causing vacuolating encephalopathy and retinopathy (VER) in larval and juvenile...

Full guide 💉 Vaccine
Whirling Disease
Parasitic 🔴 Fatal
🦠 Myxobolus cerebralis

A severe myxozoan parasitic disease of salmonid fry caused by Myxobolus cerebralis, which invades ca...

Aeromonas hydrophila Infection (MAS)
MAS Bacterial 🟠 Severe
🦠 Aeromonas hydrophila

A motile Aeromonas septicaemia (MAS) caused by Aeromonas hydrophila, an opportunistic pathogen that...

Full guide ✓ Treatable
Branchiomycosis (Gill Rot)
Fungal 🟠 Severe
🦠 Branchiomyces sanguinis, B. demigrans

A oomycete infection causing necrosis and rotting of gill tissue, associated with warm, oxygen-deple...

Cardiomyopathy Syndrome
CMS Viral 🟠 Severe
🦠 Piscine myocarditis virus (PMCV)

A chronic cardiomyopathy of large sea-water farmed Atlantic salmon caused by PMCV, characterised by...

Columnaris Disease
Bacterial 🟠 Severe
🦠 Flavobacterium columnare

A gram-negative bacterial disease causing cotton-wool-like yellow lesions on the skin, gills, and fi...

Full guide ✓ Treatable
Enteric Redmouth Disease
ERM/Yersiniosis Bacterial 🟠 Severe
🦠 Yersinia ruckeri

A systemic Yersinia infection of salmonids characterised by reddening of the mouth, jaw, and opercul...

Full guide ✓ Treatable
Epizootic Ulcerative Syndrome
EUS Fungal 🟠 Severe 🔔 Notifiable
🦠 Aphanomyces invadans (primary); secondary bacterial and Saprolegnia infections

A seasonal ulcerative disease of fish caused by the oomycete Aphanomyces invadans, producing deep, i...

Francisellosis
Bacterial 🟠 Severe
🦠 Francisella noatunensis subsp. orientalis (tropical) / noatunensis (cold)

An emerging granulomatous disease of fish caused by the intracellular bacterium Francisella, forming...

Infectious Pancreatic Necrosis
IPN Viral 🟠 Severe
🦠 Infectious pancreatic necrosis virus (IPNV)

A birnaviral disease of salmonids causing necrosis of pancreatic acinar tissue and severe enteritis...

Full guide 💉 Vaccine
Nocardiosis
Bacterial 🟠 Severe
🦠 Nocardia seriolae

A chronic granulomatous disease of marine fish caused by the filamentous bacterium Nocardia seriolae...

Proliferative Kidney Disease
PKD Parasitic 🟠 Severe
🦠 Tetracapsuloides bryosalmonae

A myxozoan kidney disease of salmonids causing massive proliferation of lymphocytes and monocytes in...

Salmon Pancreas Disease
SPD/PD Viral 🟠 Severe 🔔 Notifiable
🦠 Salmonid alphavirus (SAV)

An alphaviral disease of farmed Atlantic salmon characterised by pancreatic necrosis, cardiomyopathy...

Full guide 💉 Vaccine
Sea Lice (Lepeophtheirus salmonis)
Parasitic 🟠 Severe
🦠 Lepeophtheirus salmonis

The principal ectoparasite of farmed Atlantic salmon in the North Atlantic, causing skin lesions and...

Full guide ✓ Treatable
Streptococcosis
Bacterial 🟠 Severe
🦠 Streptococcus iniae, S. agalactiae, Lactococcus garvieae

A systemic bacterial infection of fish caused by Streptococcus and related gram-positive cocci, caus...

Full guide ✓ Treatable
Tenacibaculosis
Bacterial 🟠 Severe
🦠 Tenacibaculum maritimum (formerly Flexibacter maritimus)

A marine bacterial disease causing extensive superficial ulcerative lesions on the skin, fins, and m...

Full guide ✓ Treatable
Thermal Stress Syndrome
Environmental 🟠 Severe
🦠 Extreme water temperature events — both thermal shock and chronic sub-lethal stress

Physiological dysfunction and mortality caused by water temperatures exceeding (or falling below) th...

Anchor Worm (Lernaea)
Parasitic 🟡 Moderate
🦠 Lernaea cyprinacea and related species

A parasitic copepod whose females anchor into the muscle of fish using forked head appendages, causi...

Full guide ✓ Treatable
Argulosis (Fish Louse)
Parasitic 🟡 Moderate
🦠 Argulus foliaceus, A. japonicus

A branchiuran crustacean ectoparasite that attaches to the skin of freshwater fish, causing puncture...

Full guide ✓ Treatable
Bacterial Gill Disease
BGD Bacterial 🟡 Moderate
🦠 Flavobacterium branchiophilum

A bacterial gill disease of salmonids caused by Flavobacterium branchiophilum, characterised by lame...

Full guide ✓ Treatable
Camallanus Worm Infection
Parasitic 🟡 Moderate
🦠 Camallanus cotti, C. lacustris

A nematode intestinal parasitic infection of freshwater fish caused by Camallanus species, with worm...

Full guide ✓ Treatable
Carp Edema Virus Disease
CEVD Viral 🟡 Moderate
🦠 Carp edema virus (CEV)

A poxviral disease of koi and common carp characterised by lethargy, oedema of gills and skin, and t...

Dactylogyrus (Gill Fluke)
Parasitic 🟡 Moderate
🦠 Dactylogyrus spp. (>400 species)

Monogenean trematodes that parasitise the gills of freshwater fish, causing irritation, mucus hyperp...

Full guide ✓ Treatable
Diplostomum (Eye Fluke)
Parasitic 🟡 Moderate
🦠 Diplostomum spathaceum and related spp.

A digenean trematode whose metacercaria accumulate in the lens of fish eyes, causing cataracts and b...

Edwardsiellosis (Edwardsiella tarda)
Bacterial 🟡 Moderate
🦠 Edwardsiella tarda

A bacterial disease caused by Edwardsiella tarda causing internal abscesses, gas-filled lesions, and...

Full guide ✓ Treatable
Epistylis Infection
Parasitic 🟡 Moderate
🦠 Epistylis spp.

A ciliate ectoparasitic infection of fish skin and fins caused by stalked peritrich protozoans of th...

Full guide ✓ Treatable
Ergasilosis (Gill Maggots)
Parasitic 🟡 Moderate
🦠 Ergasilus sieboldi and related species

A parasitic copepod infection of fish gills caused by female Ergasilus copepods, which attach perman...

Full guide ✓ Treatable
Heart and Skeletal Muscle Inflammation
HSMI Viral 🟡 Moderate
🦠 Piscine orthoreovirus (PRV-1)

A reoviral disease of farmed Atlantic salmon causing inflammation of the heart and red skeletal musc...

Hole-in-the-Head Disease
Parasitic 🟡 Moderate
🦠 Spironucleus vortens (and/or Hexamita spp.)

A chronic parasitic condition of cichlids and other tropical freshwater fish caused by flagellate pr...

Full guide ✓ Treatable
Ichthyophonus Infection
Fungal 🟡 Moderate
🦠 Ichthyophonus hoferi

A systemic infection caused by the mesomycetozoean Ichthyophonus, forming granulomatous cysts throug...

Kudoa thyrsites (Soft Flesh Syndrome)
Parasitic 🟡 Moderate
🦠 Kudoa thyrsites

A myxozoan parasite that invades the muscle of marine fish, releasing enzymes post-mortem that cause...

Nephrocalcinosis
Environmental 🟡 Moderate
🦠 CO2 supersaturation in water (>20 mg/L); also associated with excess dietary calcium

Deposition of calcium carbonate and calcium phosphate crystals in the kidney tubules of fish exposed...

Full guide ✓ Treatable
Nutritional Cataracts
Environmental 🟡 Moderate
🦠 Dietary deficiency (zinc, methionine, riboflavin, tryptophan) and/or UV radiation

Opacification of the lens of the eye in farmed salmonids, primarily caused by dietary deficiency (es...

Full guide ✓ Treatable
Pseudomonas Septicaemia
Bacterial 🟡 Moderate
🦠 Pseudomonas fluorescens, P. anguilliseptica

An opportunistic bacterial septicaemia caused by Pseudomonas species, typically striking immunocompr...

Full guide ✓ Treatable
Sleeping Disease
SD Viral 🟡 Moderate 🔔 Notifiable
🦠 Sleeping disease virus (SDV / Salmonid alphavirus 2)

A togaviral disease of freshwater rainbow trout characterised by fish lying on their sides at the po...

Full guide 💉 Vaccine
Trichodina (Wheel Animalcule)
Parasitic 🟡 Moderate
🦠 Trichodina spp.

Saucer-shaped ectoparasitic ciliates that rasp the skin and gills of fish, causing irritation, mucus...

Full guide ✓ Treatable
Anisakiasis (Herring Worm)
Parasitic 🟢 Mild
🦠 Anisakis simplex, Pseudoterranova decipiens

A zoonotic nematode larva found coiled in the muscle and viscera of marine fish; causes anisakiasis...

Full guide ✓ Treatable
Fin Rot
Bacterial 🟢 Mild
🦠 Aeromonas spp., Pseudomonas spp., Vibrio spp. (polymicrobial)

Progressive necrosis and erosion of the fin margins caused by a mixed bacterial infection, typically...

Full guide ✓ Treatable
Lymphocystis Disease
LCD Viral 🟢 Mild
🦠 Lymphocystivirus (LCDV)

An iridoviral disease characterised by dramatic hypertrophy of individual infected cells (fibroblast...