Identifying Fish Ailments - Coles Pond Store
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Pond Owners Handbook

Identifying Fish Ailments

Fish – just like most living things – can get sick, or infected, and eventually die. While there are a myriad of potential problems that could potentially affect your fish, here are the usual suspects and how to take care of them.


  • Parasites
  • Bacterial Infection
  • External Fungus
  • Disease

Before taking any course of action, ensure your water parameters are in check, see our water quality guide here for more info. Fish will stay healthier and recover faster in an ideal environment.


Parasites are nearly ever present in Ponds because of their near constant exposure to incoming animals, and environmental factors. Stress, caused by injury, disease, predation, poor water quality or environmental changes can all increase a fish’s susceptibility to health issues including parasites.  Identifying parasites can be difficult at first, but will manifest in visual symptoms after a short time (approximately a week post infection). Fish will start by scratching their bodies and fins against rocks. Parasites can and will often kill even healthy fish if left untreated. Treat most parasites with COPPER in a quarantine pond or tank, alternatively dose SALT at a rate of 1.5 lbs. of POND SALT per 100 gallons after removing plants, or treat the whole pond with Formailin TETRA MEDICATION Formaldehyde and Malachite Green.[bgarea]

Minolta DSCIch, White Spot

The most common deadly parasite is Ichthyophthirius multifiliis, better known as: Ich. White spots will begin to form on the fish and grow into more opaque white spots that look like someone has sprinkled your fish with salt. Follow normal parasite treatment procedures.

Grey Spot

Costia Necatrix will manifest very similar to Ich. Fish will start with a persistent scratching, and start developing gray patches the fish’s  body. Follow normal parasite treatment procedures.

Gill Flukes

Flukes will show in the form of partly open or fast pumping gills. Gills may also appear a deeper shade of red.  Before treating, ensure water quality as these symptoms may manifest from poor water quality.  Follow normal parasite treatment procedures if water quality is good.[/bgarea]


Bacterial infections are can often be attributed to stress caused by injury, disease, predation, poor water quality or environmental changes.  Bacterial issues are relatively easy to spot if the issue is external, which is more common. You can expect to see sores or ulcers on the body, as well as what appears to be rotting flesh on orifices and fins. If the bacterial issue is an external infection, other symptoms like lethargy and erratic behavior will be noted before any physical change in the fish. Because their are so many different types of bacterial issues, there are a wide variety of treatments available. A course of broad spectrum anti-biotic via medicated food or dosing, in combination with Melafix and/or Pimafix can often cure infected fish if caught early enough. In more serious cases Dips, topical rubs, or direct injection of antibiotics.[bgarea]

fish-ulcerSkin Ulcers

Skin ulcers will manifest when a fish’s scales have been damaged to reveal the delicate tissue underneath. Scrapes, cuts, and burns (yes, burns) can all lead to an ulcer. Slowly the fish’s scales will begin to open up and reveal a red sore that can continue to grow. As the infection worsens the fish’s ability to maintain decreases and the fish can acquire secondary infections. Skin ulcers can kill a fish. Treatment with MelaFix and PimaFix can treat small ulcers, for more advanced ulcers a product called AquaGel should be applied to the wound until healed.

Fin Rot

Fin rot is apparent from it’s outset. Opaque white sections will appear on the edges of the fish’s fin(s) and the fins can begin to appear ragged. As the infection progresses, the soft membrane will disappear leaving only the tougher rays behind. Fin rot can lead to secondary infections and in turn lead to death of the fish. Follow standard bacterial treatment procedure with Mel & PimaFix.

Mouth Rot aka Mouth Fungus aka Columnaris

Mouth rot or Fungus (Columnaris) is a just another bacterial infection, not a fungus at all. It gets it’s name from the cottony white growth that accompanies the infection, which looks very similar to a fungal infection. Columnaris just like any other bacterial infection is nearly ever present, and only rears it’s ugly head when provided the opportunity. Treat as any other bacterial infection.

fish-rotBacterial Gill Disease

A fish’s gills – unlike it’s body – are difficult to see. A fish suffering from BGD can show heavy respiration, spending time in high oxygen areas of the pond (waterfalls, fountains, airstones), lethargy, and lack of appetite. These symptoms are all fairly common across several diseases, because of this closer inspection must be done before reaching a BGD diagnosis. A fish with BGD will have gills that look damaged and discolored, as opposed to a healthy fish’s bright red. Treat as any other bacterial infection, and aerate heavily. As a note, BGD is often caused by gill flukes, and should be treated as well.[/bgarea]


Fungal infections like most infections are purely opportunistic, usually a secondary infection. A fungal infection should not occur in high quality water, with the proper parameters. Fungus will take hold on a fish only when the fish’s mucus layer has been damaged, exposing scales or flesh underneath. Fungus looks distinctly different than bacteria because as opposed to looking like a solid fuzzy cloud, it looks like many single strands growing out and getting tangled. If left untreated fungus can kill a fish and lead to secondary infection. Fungal infections should be treated with TETRA FORMALDEHYDE TREATMENT, in a quarantine container or pond.


Fish fall to other ailments that can’t be attributed up to bacteria, fungus, or parasites. Some other fish ailments you may encounter are below.


Fish simply get old and die. They will display lethargy and clamped fins when near death. The fish will be this way until it passes.


Fish can ‘bloat’ around the middle. This primarily happens in fancy Goldfish, where years of selective breeding have squeezed their innards into a smaller space. If a fish it’s too much food at once – particularly dry food – and the food either swells, or releases gas while in the gut this can push against the swim bladder. This pressure on the bladder combined with compacted foods in the gut can cause the telltale signs of bloating and floating. To clear bloat up, simply stop the fish from feeding for about two days. Alternatively a high fiber vegetable like peas can be fed to help speed up the clearing. Bloat can also be caused by bacterial infection, so if none of the methods listed work after about two days, proceed as you would with a normal bacterial infection.

For more in depth learning, here is a great starting point.