Common Names: Cancer
Neoplastic growths
Malignant tumours (aggressive, reproduceable)
Benign tumours (passive)
fibrosarcoma (in fibrous tissue)
chondroma (in cartilage)
ganglioneuroma (in nerve tissue)
neuroblastomas (malignant nerv
Salinity: Freshwater
Description: Cancers in fishes are a huge subject, too lengthy to enter into here in their entirety. Here follows a brief description of possible causes and information that will attempt to help with the diagnosis of cancer under the understanding that all but the most obvious cancers can only be identified conclusively for type and effect after proper sample testing with the help of a laboratory.

Causes of cancer:

Most cancers are genetic, but piscines may have incidences of cancer inflicted upon them by many chemicals that have a carginogenic effect and a few gene altering viruses may also cause cancer. Most of the carcinogenic chemicals that effect fish are usually pollutions from farm spill hitting watercourses such as fertilizer, weekdkillers and pest control substances. In some countries , usually "third-world" countries, hunregulated heavy industry will also be responsible for periodic release of carcinoma causing chemicals. This is obviously of concern to people who's wild caught specimens come from such areas, and it should be noted that such fish , should hey become feeder items will directly poison the predator species . Many heavy metals like mercury for example can cause cancer if injested, and are never expelled by the body, meaning the fish retains the toxin all of its life.

Genetic propensity: As stated the most common cause is genetic, fish are especially vulnerable to cancers that develop particularly within the black and red pigment cells. Cave and albino fish if kept exposed to high level uv lights have no ultraviolet blocking protiens or keratinous structure in the scales to reflect light, and they too may suffer cancers as a result of uv damage. Red and black pigment cell cancer are probably the biggest single concern to fishkeepers. Selectively bred fish, untempered by natural selection, often suffer pigment cell deformities. Errors in cell replication in those areas often cause skin melanomas to arrive, and in fish like the "dalmation" molly for example, most of the cancers that develop are malignant, and eventually spread throughout the fish's body, effectively killing it. The same is true of some goldfish,koi, platies, gouramies, guppies, and many other commonly selective bred fish. The only way to avoid these inbred issues ids simply not to buy or encourage fish of excessively selectively bred origin. In some groups mortality for specimens over 2 years of age is total, with cancer becoming the primary cause of death, overtaking even bacterial concerns. This is in stark contrast to wild fish, who typically suffer morbidity by cancer in less than one percent of entire populations.

Genetic altering disease:

Papilloma viruses are unusual in that they can genetically damage tissues on the host fish and may cause cancer at any time. They are usually confined to specific species of fish, and not of major concern to the aquarium hobby. The virus is usually ingested via cannibalism of the flesh of siblings, rivals and mates in a few highly territorial species. The viruses produce enticing cystic growths on fins and appendages rather like cauliflower disease does. This is an effort to create an enticing target for fin nipping fish, thus allowing its transition from one fish to another.


Cancers can invade any part of a host body, and any and all tissue may be affected, but for the fishkeeper, for whom his or her charges have no effective chemical therapy available, only two major prerequisites about cancer need really be known, namely "Is it malignant, and likely to spread?" and " Does it need removing?". Cancers range from small granulomas, which are little more than dark speckles, all the way up to whopping huge lumps the size of the animal itself. Some scarier looking cancers actually develop their own organs, and have been known to grow their own bones and teeth! Usually though a skin cancer (usually the only kind visible in fish) will be a lump on the skin, either body coloured or looking rather like a pinking everted organ, with its own blood supply. Some cancers may be grey, and look like little bits of gum attached to the fish, some may be perfectly sealed, others may fester and suppurate and leak fluids. These are the hardest to decipher, often looking like parasite cysts or foetid wounds.

Apart from exceptional cases , identifying cancers is not easy.
Symptoms: Spots
Treatment: Only external cancers are usually tackled by veterinary surgeons,in regard to fish, many benign growths only needing to be nicked off, a little of the surrounding tissue removed, and the bleeding staunched. It is not advised that any fishkeeper try this in a domestic situation though, even if the lump looks like it may be easily removed as many may be connected to arteries and veins, and if the tumour is hastily removed, the fish may die of blood loss. Benign tumours of fin tissue are often the most easily removed.

Since chemical treatments are not available for cancer in fish, (largely down to economics unfortunately) a fish diagnosed with malignant growths that cannot be removed will eventually die, and its suffering should be ended by euthanasia. Benign growths however are usually not a significant risk to fish health, unless they become capacious enough to affect the motility or weight distrubution of the fish.

Palliate care: For fishes with cancer that a vet or owner has not elected to euthanise, efforts should be made to keep the immune system high with vitamin c enriched foods and excellent care. Expossed cancer tissue may be more open to infection than the fish itself, and may distrubute those infections to the fish. Cancers also feed on the host, growing, and taking up a proportion of the energy ingested by the fish. It may be necessary to compensate for this dietarily in order to keep the fish in otherwise good condition.
Comments: Fish can be merciless persecutors of the afflicted fish, some cancers seem to act with a magnetic attraction to fish, and disgusting as it may seem, other fish may try to eat parts of a visible cancer. If your fish is harried in this way then you should segregate it, particularly if there is a serious risk of bleeding. By way of a small tale though, the author owned a sunset platty that had the rather capacious cancer on its tail removed by a hungry tiger barb. It actually did the platy a service, and the tail regrew normally, probably far better than if the cancer had been removed professionally. The tiger barb was none the worse for his disgusting meal.

Cancers are not commonly transmittable, only the poisons and the extremely rare viruses are. For the average fishkeeper, there is no need to segregate a fish from community because it has cancer, and for shoaling species, you may as well let them live out their lives with their cagemates, unless of course , their suffering becomes intolerable. Do not be too quick to euthanise if the fish is not obviously suffering. Many fish live with cancers all their lives and many reach great ages. A malignant tumour however will force your hand to euthanasia soon enough. If a cancer isnt accelerating quickly there is no need to panic.

For genetic health of the offspring, fish that have cancer should not be bred from. A piece of advice that unfortunately many selective breeders do not follow, the result is fish that suffer from cancer in the thousands, and some very short lived specimens, and very upset owners worldwide. It is a great shame.
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Submitted By: longhairedgit
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