Guppy Fish - The Best Aquarium Pet

Guppies, guppies, guppies!


Fungus is actually a colourless plant which appears as a whitish cotton-wool look on the guppy body or fins. Fungal diseases normally only attack weak guppies where they have had damage to the skin or gills, or when the guppy's slime layer has been weakened for some reason (such as a previous bacterial problem). Fungus also occurs when guppies are kept in tanks that are too cold. Saprolegnia fungus seems to be a culprit in the death of fry, attacking the guppies' gills and causing massive deaths even before symptoms show.

Cure: Salt, Malachite Green, Methylene Blue

Mouth Fungus

This appears as a white edge around the guppy's mouth. This is usually columnaris (a bacterial disease) in most fish, but in guppies and other livebearers, it is usually a true fungus. Treat as fungus, however, keep in mind that it may be Columnaris.

Cure: Salt, Malachite Green, Methylene Blue

Fin Rot

This seems to generally be a bacterial problem in guppies, however fin nips by aggressive tank mates or damage from sharp ornaments can cause physical damage to the guppy's tail and fungus sets in. A fish with an obvious bite out of it's tail or a split that has acquired a white edge, has been infected by fungus.

If there has been no obvious damage to the tail and the edge shows disintegration and shredding (usually with a light-coloured edge), it should be assumed to be a bacterial infection.

Cures: Tetracycline, Maracyn or Maracyn Two


There are two forms this takes but both look similar, and both are caused by a bacterial infection. With one, the guppy's scales protrude from the body (like a pine cone) and with the other, the body swells with fluid which causes scale protrusion and protruding eyes. Unfortunately, it is extremely difficult to cure. The fish should be isolated immediately, and destroyed if its condition does not get better. By the time the scales protrude, the guppy's internal organs including the liver have been damaged to the point of no return. The cause is what the fish keeper should investigate to avoid another case of dropsy. Poor water conditions, weakened fish and feeding too many bloodworms may also be part of the problem.

Cures: Antibiotics


This looks similar to fungus, but is actually caused by one of two types of gram-positive bacteria.  Its causes are not really understood, but it may arise due to crowded tanks, poor water conditions, inadequate filtration, or poor water circulation (aeration).  It manifests itself in the beginning of the disease as a whiteish area where the pigment appears gone, usually on the peduncle or the body's middle area ("saddleback columnaris").   The guppy will later show difficulty swimming as the guppy's body slowly becomes paralyzed.  Most often this affects female guppies for some reason, and it is highly infectious -- it can destroy all the fish in the tank if the affected guppy is not removed. 

Cures: Formalin, Maracyn

Fish Tuberculosis

Also appropriately named the Wasting Disease. Fish stop eating, become hollow-bellied, emaciated, grow ulcers, eyes protrude, fins rot, colours pale and the guppy becomes inactive. Guppies may live months in such condition. All symptoms will not appear, but be cautious if more than 2 show. TB is caused by mycobacterium bacteria, and is passed from fish to fish by feeding on dead infected fish and feces. Guppies can pass TB to the guppy's offspring as well, so it is particularly dangerous and action must be immediate. Remove the diseased fish for observation. If there is no improvement, destroy the guppy. Be sure to remove any dead or dying fish from the tank, and quarantine completely. If a number of fish die from TB, tear down the tank and disinfect everything with bleach. TB outbreaks can usually be avoided with proper environmental conditions. TB bacterium is pathogenic to humans. Do not reach into the tank water with bare skin, especially if you have any damaged skin, and never touch a sick/dead fish with bare hands.

Cures: Antibiotics

Body Sores

Sometimes, due to aggressive behaviour, netting, shipping, etc., guppies can get damaged bodies and fins. Bacterias can then enter the guppy's body through the injury.

Cures: Melafix, Methylene Blue


Caused by bacteria that grow in the guppy's blood, this disease appears as lesions, ulcers or sores on the guppy's body, reddening at the base of the fins and the vent. The fish will eventually stop eating and may darken in colour. Ulcers may get a secondary infection of fungus. It may be a latent infection, which breaks out when fish are crowded, shipped, or handled roughly. It is important to isolate the fish since they release pathogenic bacteria directly into the water and other guppieswill be infected.

Cures: Maracyn, Antibiotics

Swim Bladder Imflammation

This is caused by a virus, which is highly infectious. The guppy or fish stops eating and cysts are formed at the rear of the abdomen. This distends the guppy's body and the fish appears to be standing on it’s head. The body degenerates and chance of recovery is low. The fish should be removed immediately and destroyed.

Cure: Salt

Ich / Ick

Often the first sign of infestation is that the guppy rubs its body against things in an effort to rid itself of the parasite. Eventually, the entire body becomes covered in white cysts that look like salt or sugar. The gills may be irritated. The parasite penetrates the skin and becomes a cyst, feeding on blood and skin cells. It grows for a few days until it drops to the bottom of the tank and forms into a cyst and cell division creates up to 1,000 zoospores, which try to attach to a fish within 70 hours - this is the infectious stage. This cycle takes about 5 days at 27°C. (the higher the temperature, the faster it's life cycle is completed). The best time to attack ich is when the parasite leaves the guppy, so raising the temperature helps to aim the medication at this stage. The fish should be quarantined for a month after treatment so they cannot infect other fish.

Cures: Malachite Green, Quinine, Formalin, Copper, Salt

Guppy Disease

There is actually a disease caused by a protozoan that is more commonly seen in guppies than in any other fish. This is a tiny parasite that attacks the skin and may even reach as far as the muscles or bloodstream. They may get large enough to resemble ich and the scales may protrude, swimming is difficult and the skin usually falls off as well. If this is not taken care of quickly it can spread throughout the tank and be very difficult to control.

Cures: Malachite Green, Copper, Formalin, Clout


Is similar to ich however these organisms are smaller, like gold-coloured dust, while ich is white, larger and more rounded. Velvet disease ("rust disease") is highly contagious. It may be difficult to see until a heavy infestation develops. Bleeding can eventually occur, with the skin peeling off. When the guppy's gills are affected the fish will have difficulty breathing and may die from asphyxiation. Velvet is a rather uncommon disease.

Cures: Copper

Excessive Slime Coating

Also called Costia, (one protozoan parasite which may be involved.) A greyish-white film of excess mucus covers the fish's body, most obviously on the eyes or darker body areas. The guppy's gills may swell and breathing appears difficult. It is caused by body parasites, which may be protozoans, monogenetic flukes, or often a combination.

Cures: Salt, Clout, Methylene Blue, Quinine, Formalin

Anchor Worm

A crustacean (copepod), it is not really a worm. It resembles a twig with a "v" on the end as the female hangs out of the guppy fish with a deep anchor. It can be up to 2 cm long and has 2 egg sacs hanging from it. The guppy can become weak and thin. The eggs are released and a hole is left in the fish which may become infected.

Cures: Organosphorous insecticide

Gill Fluke / Gill Worm

The symptoms are reddened/inflamed/bleeding/slimy gills, growths, and heavy breathing near the water surface. The guppy's gills will bleed and the guppy will have trouble breathing.

Cure: Organosphorous insecticide, trichloromethyl, Formalin


These are smaller than anchor worms, too small to be visible to the naked eye. There are several types of flukes (monogenetic) that show up on guppies. These are all flatworms that grow only as long as 1 mm in length. Younger guppies are particularly affected due to their size and action must be immediate.

Cure: Organosphorous insecticide, trichloromethyl, Formalin

Body Flukes

These seem to be common in guppy tanks. Usually the first symptom a guppy shows is scratching on ornaments or the bottom in an effort to rid itself of the parasite. Guppy fry normally display closed tails, or "pin tail". The tail may completely fall off. Heavy infestations cause a grayish look to the skin, sometimes even inflammation and redness. Usually fry are dead before they succumb to this symptom.

Cure: Organosphorous insecticide, trichloromethyl, Formalin

Internal Parasites

These are nematodes, also called roundworms or threadworms. The most commonly seen in guppies is Camallanus, which can reach up to 2 cm in length. They are reddish-brown or orange, and can be seen protruding from the guppy's anus like a tiny paintbrush. Other intestinal worms usually do not pose a threat in aquariums since they have a rather complicated life cycle, but Camallanus nematodes are capable of passing from one fish to another.

Cures: anthelmintic treatment, Jungle's Internal Parasite Guard, Pepso food, Tetra's Anti-Parasite Medicated Flakes, garlic


This condition may lead to blindness and loss of the guppiy\s affected eye(s). The cause of this disease is hard to determine. All you can do is hope that it goes away.

Cures: Unknown

Swim Bladder Disease

Unnatural, uncontrolled swimming or floating on an angle. Guppies are not prone to this problem, however it does occur, usually after a stress-related experience. It is difficult to determine the cause for this, but it seems that moving a fish from shallow water to deep water can trigger it, and poor water quality can cause it as well.

Cure: Salt