Fish Diseases

Last updated on September 12, 2010

For information related to husbandry, look in the fish biology section.

Non-infectious diseases{3982}

Factor	Source	Effects on fish
Low O₂ tension	overcrowding, water flow, low gas saturation, high oxygen demand, algal bloom	Marked decrease can kill all fish
Gas supersaturation	groundwater saturated with nitrogen, leaky valves, over-aeration of tanks	Bubbles in choroid of eye, leading to blindness; activate clotting cascade; "Gas bubble disease" when air bubbles out in fish gills: open mouth breathing, hemorrhage around gills, exophthalmos, sudden death{4764}
High un-ionized ammonia	fish metabolism, rotting food, ineffective biofilters	Gill lesions?, growth suppression
High nitrite	polluted water, poor biofiltration	Methemoglobin, hypoxia, vasodilation, circulatory collapse
High CO₂	poor filtration	If chronic, nephrocalcinosis, swim bladder dilation
High temperature	Mixing of water source	Poor research results due to stress
Rancid food	Old food, possibly with Aspergillus flavus aflatoxin B1	Poor food consumption, hemolytic anemia, hepatic necrosis; aflatoxin induces liver tumors esp. in rainbow trout

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Bacterial and Fungal Diseases of Fish{3982}

Pathogen	Disease name	Signs	Environmental cause
Flavobacterium branchiophila	Bacterial gill disease	Gill disease, resp. distress in salmonids	Overcrowding, poor water
Flexibacter columnaris	Columnaris disease	Dermal and branchial necrosis	Water too hot, high organics
Flexibacter psychrophilus	Coldwater columnaris, bacterial cold-water disease	Dermal necrosis, anemia in salmonids	Water too cold, high organics
Aeromonas salmonicida	Furunculosis	Dermal ulcers, septicemia, esp. in salmonids	Stress, hot water, carriers
Aeromonas hydrophila	Motile aeromonad septicemia	Dermal ulcers, septicemia	Hot water, high organics
Vibrio anguillarum, V. damsela	Vibriosis	Dermal ulcers, septicemia in marine fish	Stress, hot water
Pseudomonas fluorescens	Bacterial hemorrhagic septicemia	Dermal ulcers, septicemia, poor frog egg quality	Stress, hot water, high organics
Pasteurella piscida	Pseudotuberculosis	Granulomas in marine fish	??
Edwardsiella ictaluri	Enteric septicemia of catfish	Catfish septicemia	Crowding, hot water
Renibacterium salmoninarum	Bacterial kidney disease	Granulomas in salmonids	??
Streptococcus faecalis, S. iniae		Septicemia in warm-water fish, meningitis, pericarditis	Crowding, warm water
Mycobacterium fortuitum, M. marinum, M. chelonae	Fish tuberculosis	Granulomas w/ acid-fast bacteria ; chronic poor growth, wasting; or acute "dropsy", scale edema (look like porcupine quills){4764}	Opportunistic, zoonotic
Saprolegniaceae		Secondary invader ; puffy white cottony material, wet mounts have non-branching hyphae with some sporangia{4764}	Dirty water, sick fish not removed

Pathogens of zebrafish appear in bold type in the tables. Clinical signs of bacterial sepsis in zebrafish: exophthalmos, increased respiratory effort, abdominal distension, petechial hemorrhage. Antibiotics can be tried, such as sulfadiazine/trimethroprim, enrofloxacin, or oxytetracycline. Water treatment can include raising the salt content, adding formalin, or in some cases malachite green. However, malachite green is mutagenic and teratogenic so should not be used in genetically modified fish or those used in such research.{4764}

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Chlamydial and Viral Diseases of Fish{3982}

Pathogen	Disease name	Signs	Environmental cause
Epitheliocystis sp.	Chlamydial branchitis	Organisms in cystic remnant of gill epithelium; hyperplasia	Carriers, cool water
Lymphocystis iridovirus	Lymphocystis	Coalescing nodules on fins and skin	Carriers, overcrowding, trauma, warm water
Birnavirus	Infectious pancreatic necrosis	Kills salmonid fry; necrosis esp. pancreatic acini	Carriers
Infectious hematopoietic necrosis rhabdovirus	Infectious hematopoietic necrosis	Kills fry and fingerling salmonids; never diagnosed in zebrafish{4764}	Carriers; cool water
Catfish herpes	Channel catfish virus disease	Septicemia	Overcrowding, warm water

Parasites of Fish {3982}

Agent	Signs	Environmental causes
Phytomastigophorea, Protozoa: Piscinoodinium(formerly Amyloodinium or Oodinium)	Velvet disease (dermatitis, branchitis) ; trophonts embed in skin and result in sloughing; zebrafish "flash" to scratch themselves and have velvety or dusty appearance{4764}	Overcrowding, warm water
Zoomastigophora: Ichthyobodo necatrix, Hexamita sp.	Costiasis: dermatitis, branchitis; enteritis in young salmonids	Binary fission, spreads quickly
Eimeria sp.	Enteritis	Rapid spread in crowded juveniles
Loma (Microspora)	Branchitis	Rapid spread
Sphaerospora salmonae (Myxozoa)	Proliferative kidney disease in salmonids	Direct contact
Ciliophora: Chilodonella, Trichophyra, Ichthyophthirius, Trichodina	Dermatitis, branchitis; multifocal, raised, 1mm white nodules on skin and gills; characteristic horseshoe shaped nuclei on wet mounts. Trichodina have characteristic rotating motion and are circular or domed on wet mounts.{4764}	Raising water temp. hastens life cycle
Metazoa: Gyrodactylidae, Dactylogyridae	Dermatitis, branchitis	Crowding; warm water speeds spread
Nematodes: Pseudocapillaria tomentosa	Usually subclinical; heavy infections cause reduced growth, wasting; diagnosis of capillarid eggs in feces{4764}

Treatment

Generally, disinfectants can be put into the water successfully, such as chloramine T, formalin, salt, quaternary ammonia compounds or aniline dyes. Antibiotics would be needed in huge quantities to be efficacious in the water, and so are added to the food or injected directly IP or IM. Viral diseases are usually treated through manipulation of water temperature.

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