Most of the time, troubleshooting by frequent water changes and avoiding fish stress will prevent serious outbreaks of disease in the tank. Off the list of preventative things, I cannot stress buying small numbers of fish SLOWLY enough; many a tank can be devastated by bringing in a large number of new fish in a relatively small time. Healthy fish can actually cohabitate with some disease organisms at low concentration without becoming symptomatic, but when fish are stressed by sudden environmental changes and overcrowded conditions, their immune systems don’t function well and they become far more susceptible to disease. New fish especially are vulnerable, because they have been passed from breeder to wholesaler to distributor to retailer to consumer and most likely spent the whole time in horrid surroundings. They should be quarantined in a separate tank whenever possible.

Some diseases can be tenacious once they take hold in a tank. Be sure to try and figure out a general diagnosis before dumping a lot of medication into the tank, as some meds are toxic dyes that can kill with overdosing (especially to sensitive fish such as tetras and scaleless cats), and some, such as antibiotics, will wreak havoc on your biofiltration and throw your established tank into a new cycle. Keep in mind that “sometimes the cure can be worse than the disease” (and ALL chemical additions to the tank which change water conditions stress the life inside the closed environment). Also, keep in mind that most plants and inverts will not tolerate many medications in the water. In planted aquaria, it is best to remove the affected fish to the quarantine tank or into a small treatment vessel with circulation and heat. It is sometimes helpful to add a small (1tbsp/5gal) amount of aquarium salt (NOT marine salt, which is different), as most medications disturb healthy gill function, and the salt reduces osmotic shock and electrolyte loss… but this is a somewhat controversial issue that I address in the following article (pros & cons): To Salt or Not to Salt?.

I’ve been working on a photo archive of fish diseases that people send me or allow me to use from their sites. This list and archive of photos is not meant to be exhaustive or comprehensive. Please note also that some diseases have multiple manifestations (Columnaris, NTD, Fish TB, to name a few), and may vary in presentation from fish to fish; others are not true “diseases” caused by a single organism, but rather signs that could point to a number of causative organisms (dropsy, pop-eye). Click on the thumbnails, and you will be linked to the larger photos (if it was larger to begin with, that is, I can’t enlarge photos any larger than they were when sent to me, because this will not improve resolution).

THIS IS AN ONGOING PROJECT THAT IS ALWAYS BEING ADDED TO. IF YOU HAVE A RELATIVELY CLEAR PHOTO OF A FISH WITH A DISEASE THAT YOU THINK I CAN USE, PLEASE EMAIL ME.

 

 


Common Name: Ich (or Ick)
Pathogen/Cause: Ichthyophthirius multifiliis (FW) , Cryptocaryon irritans (Marine counterpart)
Physical Signs: Distinct, sometimes slightly-raised white spots that look very similiar to grains of salt or white sand on the skin.
Behavioral Signs: Scratching against objects (skin irritation), clamped fins, may “hang” and gasp near surface if infection reaches the gills.
Potential Treatment: Numerous treatments: brand names include Mardel’s Maracide or Coppersafe, Jungle’s Ick Guard, Aquarium Pharmaceuticals’ Super Ich Cure, treatments that contain formalin, etc. Take special note of warning labels; copper is not safe for invertebrate animals or plants, malachite green (ingredient in large majority) is dangerous for scaleless fish and many small tetras (halve dosage). Marine formulations slightly different. Most medications not tolerated well by corals and inverts. Best treatment for marine fish is QT, feeding garlic and use of cleaner fish/shrimp.
Other Notes: Perhaps the most common disease of pet fish. Tends to attack stressed fish, especially with rapid temperature and pH fluctuations. Easily treatable with caution if caught in time, but may be recurrent if not treated for at least a week. Cysts live in gravel, has multiple life cycle stages, read my article for more treatment options. Water changes, raising temperature (to speed life cycle), darkening of tank, etc. all recommended. Guard for secondary infection of wounds by bacteria.Certain fish, such as gymnotoids (FW), hatchetfish (FW), batfish (SW) and tangs (SW) especially susceptible.
Photos:

 

Ick

Ick

Courtesy of Anonymous (left the photo big, so you can see very nice close-up of individual ich spots)

Ick
Ick
Courtesy of Dave Pettit (please note: not typical of this disease, since larger spots likely represent coalescence of individual grains, also seen on dorsal fin; in addition, possible coinfection with lymphocystis)
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Common Name: Velvet
Pathogen/Cause: Oodinium limneticum, Oodinium limneticum (FW) , Oodinium ocellatum (Marine counterpart)
Physical Signs: Powder-like white, grey or gold dusting on surface of fish (finer than ich, more similiar to the consistency of talc).
Behavioral Signs: Scratching against objects (skin irritation), clamped fins.
Potential Treatment: Aquarium Pharmaceuticals General Cure, Jungle Velvet Guard, also, many of the same cures for ich and other parasitic diseases will work.
Other Notes: Same warnings for treatment as with ich.
Photos:

velvet

Courtesy of Shawn Prescott

velvet

Courtesy of Qian Hu Inc.

velvet

Courtesy of John Woodall.

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Common Name: Hole-in-the-Head Disease (HITH)
Pathogen/Cause: Spironucles sp. and Hexamita sp.; debatable and controversial whether they are the true pathogens that cause it.
Physical Signs: Holes that widen the sensory pores in the heads of large fish (this in itself is more aptly ascribed to HLLE, head and lateral line erosion, which in turn is related to a variety of water quality factors, not necessarily an infectious parasite). May exude pus.
Behavioral Signs: Often asymptomatic until serious; general signs of lethargy, may have trouble swimming due to loss of balance.
Potential Treatment: Medications that contain mentronidazole; Brand names: Jungle Hole-N-Head, Aquatronics Hex-A-Mit, Aquarium Pharmaceuticals General Cure, etc.; however, there is controversy over whether or not the parasite is the major causitive factor, medication may not be necessary; see information linked at right.
Other Notes: Watch for secondary bacterial infections. Often attacks large fish fed with live foods. Cichlids are especially susceptible. Please check World Cichlid’s page on HITH/HLLE which has much more detailed info, theories, and potential treatments of this disease. Also, Dr. Barb’s Flippers and Fins Site has some more info for curious minds.
Photos:

 

hole in the head

Courtesy of Pet Care Forum

hole in the head

Courtesy of Adam of World Cichlids

hole in the head

Courtesy of Trish Laam (mild case shown)

hole in the head

Courtesy of Anonymous

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Common Name: Neon Tetra Disease (NTD)
Pathogen/Cause: Plistophora hypessobryconis
Physical Signs: Loss of color in the red stripe and/or milky/brownish coloration, pale area beneath the dorsal fin.
Behavioral Signs: Sluggishness, erratic swimming, separating from the school, weight loss, occasionally in advanced stages ends in a secondary bacterial infection that causes bloating and pop-eye.
Potential Treatment: No known dependable and consistent cure, though many claims are made.
Other Notes: NOT species specific to the neon tetra. May also infect other small tetras and fish such as danios. Highly contagious, usually considered incurable (some claims made, no proven studies confirm them), and inevitably fatal. Quarantine suspect animals immediately.
Photos:

 

neon tetra disease

Courtesy of Not Catfish

neon tetra disease

Courtesy of Qian Hu Inc

neon tetra disease
Courtesy of Mona Holmstrom (although NTD typically affects the red stripe of these tetras, this shows that it can sometimes discolor the stripe of blue irridescence through tissue erosion)
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Common Name: Bacterial Fin Rot
Pathogen/Cause: Various organisms (nonspecific)
Physical Signs: Shredded-looking and tattered fins decreasing in length, sometimes infected down to the pedicle.
Behavioral Signs: Increasing difficulty swimming, behavioral signs depend on whether other secondary infections present.
Potential Treatment: Broad spectrum antibiotics.
Other Notes: Frequent water changes a must to improve quality. Test for ammonia, nitrites, nitrates.
Photos:

 

Bacterial Fin Rot
Courtesy of Anonymous
Bacterial Fin Rot
Courtesy of Judith de Vos (mantis) of The Age of Aquariums

Bacterial Fin Rot

Courtesy of Qian Hu Inc. (also shows bad bacterial infection on rest of body.)

Bacterial Fin Rot

Courtesy of Vincenzo “Noodles” Nood

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Common Name: Pop-Eye
Pathogen/Cause: Various organisms (nonspecific), Severe Stress
Physical Signs: Exopthalmos (protrusion of the eyeball from the socket) caused by accumulation of pus and fluid in the infected orbit.
Behavioral Signs: Associated with loss of vision, also just general signs of lethargy.
Potential Treatment: Broad spectrum antibiotics. Many formulations available. For a more thorough discussion on the various causes & treatments of popeye, please refer to Dan’s archived comments about popeye.
Other Notes: Frequent water changes a must to improve quality. Test for ammonia, nitrites, nitrates. Pop-eye is a sign of a number of infections, rather than a disease in its own right. For more on this disease, read this.
Photos:

  Pop-Eye

Courtesy of Qian Hu Inc.

Pop-Eye
Courtesy of Pet Care Forum
Pop-Eye
Courtesy of Joe Azzopardi (Jazzo) of The Age of Aquariums
Pop-Eye
Courtesy of Anonomous (also illustrates dropsy)

 

Common Name: Cloudy Eye
Pathogen/Cause: Various organisms (nonspecific), Severe Stress, Malnutrition, Cataracts, Old Age, Hyperproduction of slime due to poisoning, bad water quality, or irritation.
Physical Signs: A cloudy white or grey “haze” over the eyes that may cause blindness.
Behavioral Signs: Associated with loss of vision, also just general signs of lethargy.
Potential Treatment: Investigate if water quality is high first (water changes), then if nutritional needs of that species are being met. Wait at least a week or two before trying any antibiotics, it will often clear on its own if water quality is high.
Other Notes: Frequent water changes a must to improve quality. Test for ammonia, nitrites, nitrates. Cloudy eye is a sign of a number of things, rather than a disease in its own right.
Photos:

  Cloudy Eye
Courtesy of Planet Catfish

Cloudy Eye

Courtesy of Qian Hu Inc.

Cloudy Eye
Courtesy of “Sharkie”
Cloudy Eye
Courtesy of Vincenzo “Noodless” Nood
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Common Name: Bacterial External Infections, Columnaris (specific to F. columnaris); Often Misnamed “Mouth Fungus”, Fish Tuberculosis/TB Skin Infection (specific to Mycobacterium spp.)
Pathogen/Cause: Various organisms. Positive diagnosis not possible outside of lab culture & microscopy (not practical for most hobbyists). Gram positive: exceedingly rare in FW fish; small handful of SW species, but most primarily do not attack skin. Gram negative: Flexibacter columnaris, Aeromonas spp., Pseudomonas spp., Vibrio spp., Salmonella spp., many others not listed. Non-stainable: Mycobacterium spp., mostly M. piscium & M. marinum
Physical Signs: White, clear, red/pink areas of necrosis. Occasionally slightly ragged/fuzzy appearence. Inflammed patches and sometimes deeper ulcers develop. Various patterns of appearence and presentation. Columnaris usually presents near the head and sides of the body and is often mistaken for a fungus; it is characteristically white and patchy.
Behavioral Signs: Various: lethargy, hiding behavior, “hanging”, clamped fins, loss of appetite, general constitutional signs.
Potential Treatment: Broad spectrum antibiotics. (Examples include but are not limited to: Maracyn I & II, Jungle Binox, Aquatronics Kanacyn, etc.). Frequent water changes a must to improve quality. Tuberculosis is difficult to treat because it attacks intracellularly.
Other Notes: Frequent water changes a must to improve quality. Test for ammonia, nitrites, nitrates. Columnaris perhaps one of the most common skin infections of pet fish (livebearer fish and certain other fish especially susceptible). Specifically for F. columnaris, read this article by Dr. Barb. Fish tuberculosis (though not transmitted by the same species that causes human tuberculosis) can be transmitted as zoonosis called “fish tank granuloma” on hands with open wounds (again, another article by Dr. Barb discusses this issue. Use gloves if reaching in the tank with suspect animals.
Photos:

  columnaris
Courtesy of Chuck’s Hobbies & Pets (shows columnaris infection)

aeromonas
Courtesy of Anonymous
(shows aeromonas infection)

ulcer

Courtesy of Qian Hu Inc.
(uncultured specimen, pathogen unidentified)

Bacterial External Infections
Courtesy of Vincenzo “Noodless” Nood
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Photos:

  Bacterial External Infections

Courtesy of Elena Wong

Bacterial External Infections

Courtesy of Michele Hartley
(uncultured specimen, pathogen unidentified)

columnaris
Courtesy of Vincenzo “Noodless” Nood
tuberculosis infection
Courtesy of Shawn Prescott
(shows tuberculosis infection)
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Common Name: Fish Tuberculosis/TB Systemic Infection
Pathogen/Cause: Mycobacterium spp., mostly M. piscium & M. marinum.
Physical Signs: Various presentations, hard to make certain diagnosis without necrospy or lab culture. Includes: wasting away, shrunken stomachs, occasionally skin infections, spinal curvature deformity in advanced cases.
Behavioral Signs: Various: anorexia/refusal to eat, lethargy, hiding behavior, “hanging”, clamped fins, loss of appetite, general constitutional signs.
Potential Treatment: Difficult to treat because it attacks intracellularly and multiplies within macrophages (the fish’s own defense system). Try a strong antibiotic such as kanamycin sulfate or streptomycin. Euthanasia must be considered in bad cases.
Other Notes: Fish tuberculosis (though not transmitted by the same species that causes human tuberculosis) can be transmitted as zoonosis called “fish tank granuloma” on hands with open wounds (see photos, below). Use gloves if reaching in the tank with suspect animals. M. marinum can be a serious skin infection in people! If a rash such as this developes, especially if you have a marine aquarium, make sure your hobby is known to your doctor. Read this article for more info.
Photos:

  Fish Tuberculosis
Courtesy of Connie from Acmepet

Fish Tuberculosis Courtesy of Mr. Chris from The Age o Aquariums
Fish Tuberculosis
My own photo (wasting looks more pronounced in real life)
Fishtank Granuloma
Courtesy of MonkeyDog from Reef Central (shows a photo of Fishtank Granuloma on the arms of a reefkeeper caused by the marine bacterium Mycobacterium marinum. Was a bad case with several complications.)
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Common Name: Dropsy
Pathogen/Cause: Various organisms (nonspecific), poor water quality.
Physical Signs: Bloated appearence with scales that stick out like a pine cone. Best viewed from above. Dropsy is not really a specific pathologic entity, it is to describe a general condition of fluid accumulation in the internal body cavity, which has many causes. Dropsy usually signals internal infection and multiple organ failure. It can be compared to ascites in humans in end stage kidney failure.
Behavioral Signs: Lethargy, lack of appetite, grave constitutional signs.
Potential Treatment: Unfortunately, dropsy is *usually* incurable and fatal; however, in rare cases, spontaneous recovery may occur. A strong antibiotic such as kanamycin sulfate can be tried, but because it is an internal infection, usually it does little good.
Other Notes: Take measures to improve water quality immediately. Fortunately, it is not highly contagious.
Photos:

  Dropsy

Courtesy of Qian Hu Inc.

Dropsy
Courtesy of Judith de Vos (mantis) from The Age of Aquariums
Dropsy
Courtesy of JoAnne Burke of PureGold
Dropsy
Courtesy of Cindy Downs (illustrates mild case that recovered with salt bath)
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Common Name: Hemorrhagic Septicemia
Pathogen/Cause: Various organisms, Ammonia spike
Physical Signs: Distinct bright red streaks on fins (caused by vascular inflammation due to systemic/bloodborne bacterial infection) and occasionally patchy red discoloration on the flanks of the body.
Behavioral Signs: Depends on severity of condition. If due to ammonia, may show in conjunction with hyperventilation (fast breathing) and gasping at the surface, erratic swimming, etc.
Potential Treatment: Broad spectrum antibiotic. Can resolve spontaneously in some fish if source of water quality problem is removed.
Other Notes: Check water quality, especially if fish exhibiting other signs of ammonia poisoning (gasping at surface). Regular water changes and measuring of ammonia/nitrite (especially if relatively new tank) are a must. In FW, commonly seen in goldfish due to their naturally high ammonia output. In SW, often seen in tangs due to their inability to tolerate sudden water quality changes and susceptibility to shock.
Photos:

 

septicemia
Courtesy of Caroline Ellis
septicemia
Courtesy of “Squiggly” (danio pictured here)

septicemia

Courtesy of Qian Hu Inc.

septicemia
Courtesy of Sylvia Bernard
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Common Name: Swim Bladder Disease
Pathogen/Cause: Various; Often indigestion in goldfish and other “balloon” breed fish, but may be bacterial infection in other species. Occasionally, sudden trauma such as when fish are jostled excessively in transit or “dumped” into water without acclimatization may result in fatal injury to the swim bladder.
Physical Signs: May show some limited bloat, but usually no real physical changes.
Behavioral Signs: Fish has great swimming upright despite active attempts to do so. May occasionally float “belly up”.
Potential Treatment: Different depending on species; goldfish are very susceptible and sometimes cured by discontinuation of diet and salt bath, followed by change in diet to high fiber digestible foods. However, other fish may require antibiotics and have a worse prognosis. Recently introduced fish that exhibited signs within a matter of minutes have the worst prognosis of all, and there is often no cure for trauma to the swim bladder.
Other Notes: Most common in “pot-belly” shaped breeds of fish, such as goldfish & parrot cichlids due to blockage and insufficient fiber/vegetable matter in the diet. However, many fish that suffer trauma or excess stress, or just get an internal bacterial infection that occurs on or around the swim bladder may have problems. Baby fish fry that have swim bladder problems are commonly known as “belly sliders” (most scoot around the bottom fo the tank, unable to swim up, or spin uncontrollably in the water). It is still unknown if this is the same exact disease entity or what the cause is, but most attribute it to congenital or developmental causes, sometimes birth defects, premature birth or inadequate nutrition at certain stages. They should be culled to prevent suffering.
Photos:

 

swim bladder disease

Courtesy of Qian Hu Inc.

swim bladder disease
Courtesy of Kevin Carroll
Swim bladder disease
Courtesy of Nick Beach (shows “twirling” behavior, a futile attempt to swim)

 

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Common Name: Enteric Red Mouth
Pathogen/Cause: Yersinia ruckerii.
Physical Signs: Red mouth and hemorrhages on the belly. Internally involves liver and spleen.
Behavioral Signs: Lethargy, lack of appetite, constitutional signs.
Potential Treatment: Little known. Lowering temperatures may improve state.
Other Notes: More commonly seen in wild caught fish at higher temperatures, much more rarely seen in the hobbyist trade.
Photos:

 

Enteric Red Mouth
Courtesy of Judith de Vos (mantis) from The Ag of Aquariums (this is a very rare disease of tropical fish, and there are other more common bacteria that infect the mouth and redden it)
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Common Name: Body Fungus
Pathogen/Cause: Saprolegnia spp.
Physical Signs: A very fuzzy growth which projects from the skin or fins of the fish. Usually has the “fluffy” appearence of food molds, can be white or grey. Needs to be differentiated from “false mouth fungus” Columnaris (see above). True parasitic fungus prefers to grow on already dead tissue and will often coexist with bacterial infections.
Behavioral Signs: Usually not severely affected until later stages.
Potential Treatment: Many formulations available, including brand names: Jungle Fungus Guard, Mardel Maroxy, Aquarium Pharmaceuticals Fungus Cure and generic formulations usually containing methylene blue.
Other Notes: Fungal infections are relatively rare but do happen in already weakened fish. They will be very distinct in appearence, as opposed to Columnaris, which is probably far more commonly seen in the aquarium (less protrusion of fibers, just a ragged fuzzy appearence). See photos to differentiate.
Photos:

 

Body Fungus
Courtesy of Chuck’s Pets & Hobbies
Body Fungus
Courtesy of Pet Care Forum
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Common Name: Cotton Fin Fungus
Pathogen/Cause: Various, often Saprolegnia spp.
Physical Signs: Cotton-like “fluffy” or wispy growth trailing on fins of fish. Can gradually promote decay of tissue.
Behavioral Signs: Usually not severely affected until later stages.
Potential Treatment: Many formulations available, including brand names: Jungle Fungus Guard, Mardel Maroxy, Aquarium Pharmaceuticals Fungus Cure and generic formulations usually containing methylene blue.
Other Notes: Prefers to attack already damaged or injured tissue. Most important action is to do water changes and increase circulation of the system. Saprolegnia prefers to live in stagnant water. Sometimes improvement of water quality alone will erradicate the disease.
Photos:

Cotton Fin Fungus
Courtesy of Jungle Labs

Cotton Fin Fungus
Courtesy of Joe from Badman’s Tropical Fish
Cotton Fin Fungus
Courtesy of Jungle Labs
Cotton Fin Fungus
Courtesy of Michele Hartley
(very bad case of fungal infection on caudal fin; likely secondary to erosion by primary bacterial infection)
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Common Name: Lymphocystis, Cauliflower Disease
Pathogen/Cause: Lymphocystis spp. (A DNA Iridovirus).
Physical Signs: Viral infection that causes cells to become megaloblastic, thus forming small tumors (bumps or growths), often along the lateral line or the pedicle, where the fin meets the body. The tumors sometimes take on the appearence of tiny cauliflowers, thus the name.
Behavioral Signs: Lethargy, general symptoms, may affect balance and swimming control if along the lateral line.
Potential Treatment: Frequent water changes and reduction of ammonia and nitrites in water may reduce stress to help the fish battle the infection and shrink tumors on its own. Interestingly, cyprinids & catfish which have been studied appear to be resistant.
Other Notes: Watch for secondary bacterial infections. Often attacks large fish fed with live foods. Cichlids are especially susceptible. Please check World Cichlid’s page on HITH/HLLE which has much more detailed info, theories, and potential treatments of this disease. Also, Dr. Barb’s Flippers and Fins Site has some more info for curious minds.
Photos:

 

Lymphocystis
Courtesy of 2la from The Age of Aquariums (not characteristic of usual presentation of disease)
Lymphocystis
My own photo (Taken at a local pet store which will remain unnamed.)
Lymphocystis
Courtesy of Tom Choi
Lymphocystis
Courtesy of Lars Lonstromm of the Laboratory of Aquatic Pathobiology
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Common Name: Solid tumors of unknown cause
Pathogen/Cause: Not fully understood in fish or man. Many oncoviruses may be suspect in turning off genes involved in tumor suppression. In fish, just as in other animals, may be benign or malignant (cancerous).
Physical Signs: Growing mass of tissue, can occur on almost any part of the body.
Behavioral Signs: Usually not overtly affected unless the tumor is very fast growing internally, or obscures vision, feeding, or swimming.
Potential Treatment: None for most fish. Seek veterinary help for large and/or expensive fish. Surgery often the only cure, though rarely will shrink back on its own.
Other Notes: Not much known about the fish oncology at this time. Watch tumor closely for fast, uneven growth of tumor. If it keeps the fish from feeding and/or swimming, consider euthanasia.
Photos:

Solid tumors
Courtesy of The Welborn Pet Hospital.
Solid tumors
Courtesy of Joel Rose
Solid tumors
Courtesy of Ron Travelbee from Badman’s Tropical Fish
Solid tumors
Courtesy of Mike Hottovy
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Common Name: Anchor Worm
Pathogen/Cause: Lernea spp.
Physical Signs: Actually, lernea is a copepod (crustacean arthropod) rather than a true worm. It looks like a small whip (a few mm to under an inch long) attached to the fish at the mouth end and with a forked tail.
Behavioral Signs: Usually none noted unless very severe with secondary infections.
Potential Treatment: May be physically removed, but will cause great stress to the animal, and must be done carefully and with a dab of antibiotic over the wound afterwards. Brand name formulations like Jungle Parasite Guard and Aquarium Pharmaceuticals may also help.
Other Notes: Rarely seen in pet fish not kept outdoors (in ponds), and usually then only in ones that have been fed live foods.
Photos:

 

Anchor Worm
Courtesy of The Dept. of Western Australian Fisheries
Anchor Worm
Courtesy of Qian Hu Inc.
Anchor Worm
Courtesy of “JJ”
Anchor Worm
Courtesy of John Childers (this photo is one of the best high-resolution photos I’ve ever seen of its kind; really captures the anatomy of this parasite in detail)
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Common Name: Fish Louse
Pathogen/Cause: Argulus spp.
Physical Signs: A flat disk-shaped arthropod parasite with many legs. On the fish itself it is barely noticeable only as a flat, dull colored bump that you may just think is a part of the fish, unless you see the legs themselves or the disk moving around on the body.
Behavioral Signs: Usually none noted unless very severe with secondary infections.
Potential Treatment: May be physically removed, but will cause great stress to the animal, and must be done carefully and with a dab of antibiotic over the wound afterwards. Brand name formulations like Jungle Parasite Guard and Aquarium Pharmaceuticals may also help.
Other Notes: Rarely seen in pet fish not kept outdoors (in ponds), and usually then only in ones that have been fed live foods. Crustacean not related to true lice, which are insects.
Photos:

  Argulus
Courtesy of Niklas Gustavsson
(beautifully clear image of fish louse out of water!)

Argulus
Courtesy of Niklas Gustavsson
Argulus
Courtesy of Qian Hu Inc.
Argulus
Courtesy of The Aquatic Animal Health Research Institute
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Common Name: Flukes (Skin, Gill, or Eye)
Pathogen/Cause: Dactylogyrus vastator (Gill Fluke), Gyrodactylus sp. (Mostly Skin Flukes), etc.
Physical Signs: Gill flukes may show with red, inflamed gills, but otherwise many fish flukes are microscopic (some of the largest being just a few mm, but mostly smaller), and so confirmed diagnosis by physical appearence alone is not possible. Confirm with a vet or lab.
Behavioral Signs: Scratching, gasping at surface (again a nonspecific sign that has other more common causes, see comments at right).
Potential Treatment: A good, thorough discussion of treatment options can be found in Dan’s archived comments on fluke treatment.
Other Notes: No photos are included here, because usually flukes are too small to visualize with the naked eye. This also creates serious problems for trying to diagnose by general physical signs (hyperproduction of slime, inflamed gills) or general behavioral signs (listlessness, gasping, scratching, etc.). All these signs overlap considerably with other more common causes of skin and gill irritation, including ammonia poisoning and more common skin parasitisms such as ich. The first step in any tank where these signs are seen is to rule out ammonia poisoning first by testing for any level above 0.
Photos:

  External parasite
Courtesy of Cindy Buors (blurry photo of worm-like parasite on gill; large for most gill flukes, which are difficult to see with the naked eye; may possibly be another type of external parasite)

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Common Name: Roundworms
Pathogen/Cause: Unknown nematode species (metacercarean form)
Physical Signs: As shown below as an infection of connective tissue (usually internal worm infections cannot be seen externally and often affect the gut; in these cases, they have migrated to muscle tissue).
Behavioral Signs: Loss of appetite, lethargy, etc.
Potential Treatment: Try Clout or an antiparastic medication for large parasites (formalin and many methods were tried on the first cases below without success). There is also some good information on the treatment of camallanus worms as contributed by Jason Parry.
Other Notes: Please read my article, Worms in my tank?? before jumping to the conclusion that any worm in the tank is a parasitic or disease causing worm. The large majority of small worms seen in the aquarium not attached to the fish are free-living and harmless (the ones shown below are an obvious exception). Most of these true parasites shown below require a fish host at some time in their life cycle. They often come in with contaminated live foods such as Tubifex worms.
Photos:

 Roundworms
Courtesy of Mike Spafford
(unknown/possible sparganosis of nematode infection attacking muscular tissue)

Roundworms
Courtesy of Mike Spafford
(unknown/possible sparganosis of nematode infection attacking muscular tissue)
Roundworms
Courtesy of Tom Lorenz
Roundworms
Courtesy of Kevin Piper (another unpleasant photo of camallanus worms protruding from a fish)
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Roundworms
Courtesy of Averi Dohr
nematode
Courtesy of Anonymous (an interesting photo sent to me; moving nematode was found between the scales of a large koi)
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Common Name: NA / Unidentified Lesions, Growths & Cysts
Pathogen/Cause: Unknown–those shown below could have a number of causes–they could be bacterial infections that formed pus-filled cysts under the skin, they could be true tumors (see above), Lymphocystis, cysts that formed around worms, etc. Because I was uncertain, I didn’t want to mislabel them, so I keep them here in the hopes that they will still help someone, if they see something similar. For a more thorough discussion of various causative organisms, please refer to Dan’s archived comments on “unknown lumps & bumps”.
Physical Signs: Varies greatly.
Behavioral Signs: Varies greatly. May have no affect on behavior at all, depending on cause. If near the mouth and it hinders eating, could have obviously faster consequences.
Potential Treatment: Unknown, may be incurable in some (if they turn out to be true tumors); depends on individual case. For those exuding pus and fluid and/or those cases where behavioral lethargy and malaise is seen, try an antibiotic. More detailed information on different treatment options that can be attempted can be found in Dan’s archived comments on “unknown lumps & bumps”.
Other Notes: These pictures shown below may span a wide range of different causes. Some are clearer than others.
Photos:

  Cyst
Courtesy of Mike Spafford (case shown above is recurrent; suspect lympho, but without certainty)

Cyst
Courtesy of Yew Wee Tan (this didn’t look like any classic “textbook presentation” of anything that I knew of, except possibly a clumping bacterial or fungal nidus on the trailing caudal fins; photo clarity didn’t permit me to say for sure… if anyone has any idea of this being more specifically characteristic of something else, please let me know)
Cyst
Courtesy of Michele Hartley (beautiful photo of a true hollow cyst; I believe that it may have originated with a bacterial infection just under the skin, and then grown enormously due to pus accumulation; fish shown above died within a relatively short time of first appearence)
Cyst
Courtesy of Luigino Bracci (amazingly clear photos of such a small, darting fish; it is beyond my knowledge what this growth could be, it was described to me as an adherant circumscribed and object that the owner believed may have been a parasite; however, it is larger than and distinct from most of the common fish parasites I am aware of)
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Cyst
Courtesy of Nick Austin(beautiful series of 3 professional-quality photos; appear to identify the same multiloculated, fluid-filled cyst)
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OTHER

Photos:

  Fight injury
Courtesy of Michele Hartley (illustrates fight injury in male bettas that jumped barrier)

Fight injury
Courtesy of Michele Hartley (illustrates fight injury in male bettas that jumped barrier)
Gravid loach
Courtesy of Kamphol (shows a normal gravid loach [the equivilent of “pregnant” for egglayers]–obviously not a disease state, used here only for the purposes of comparison with pathologic causes of bloating)
Skin injury
Courtesy of Nathan Cantrell (superficial skin injury secondary to trauma; likely at this point not yet seriously infected, but may be in a subacute time frame)
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Badman’s note. Pandora an old friend of the site is currently unable to further her work and her former webhost is on a temporary Hiatus. Working with her former host and friend I was able to recreate much of Pandoras hard work and once again offer most of this valuable resource to all hobbyist. I cleaned up the tables some and removed any broken links, all text is original.

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