Most Common Fish Diseases and How To Prevent Them

Adding fish to your pond can add an interesting and beautiful element but fish need the right habitat to survive. They can be plagued with diseases and the best way to avoid this is pond maintenance and prevention. We will discuss the most common fish diseases and prevention techniques that will keep your fish happy and healthy.

Fish should be observed every day, if possible, to detect signs of disease. The following are the most common diseases to plague pond fish:


Finrot is often seen in pond fish and can be detected if their fin edges are white and the fins become ragged and streaked with blood and appear like they are being "eaten away”. This is precisely what the bacteria that cause the disease are doing.


If your fish are bloated and have protruded scales this can be a sign of Dropsy, a bacterial infection of the kidneys, which causes fluid accumulation or renal failure. It appears to create problems only in weakened fish.

Skin Ailments

A number of skin ailments are common in pond fish. If fish are rubbing against underwater objects and jumping, it can be an indication their skin is irritated by parasites. In severe cases, like Clamped Fin, they swim in a listless fashion with fins folded against their body and are often isolated from other fish. If you look closely you may find a slimy coating over the body or in patches, which are particularly obvious against dark areas of the body and eyes. Poor water quality, skin and gill parasites (for example: protozoans like costia, chilodonella, whitespot), and flukes (flatworms approximately 1mm long) may cause the irritation.

Fungus is another skin ailment that appears as tufts of white that look like a "cotton wool" material and usually develop in patches on the fish's body. This secondary bacterial infection is a sign of damage.

Ick, also known as Whitespot, is exactly what the name implies, small white spots on the fins and body of your fish. Due to its complex lifecycle, this parasite must be killed with seven-day treatments. On day one, treat your pond with a broad-spectrum remedy. Seven days later, repeat after a 20% water change. Repeat treatment at seven daily intervals if necessary.

Most of these ailments can be cured with a broad-spectrum treatment and a clean habitat. You can also use a salt dip for sick fish. Sick fish should be removed from the pond to a treatment container, like an old wading pool or aquarium, to prevent disease spreading to the other fish. Make an un-iodized salt dip by using Pond Salt. Gently place fish in a soft nylon net, then lower them into the salt dip for 5 to 10 minutes. After the dip, a majority of microscopic parasites that are lethal will drop off the fish. Salt dips are the least toxic method and quite effective.

Prevention is key in maintaining healthy fish and there are three main practices that can minimize the possibility of disease outbreaks. These are maintenance of good water quality, proper nutrition and elimination of contact with wild fish whenever possible. Also important in prevention is controlling related "environmental" stressors. Stress may result from a variety of conditions, including overcrowding, poor water quality, inadequate nutrition and weather-related environmental stress. Common water quality stressors are low dissolved oxygen and/or a buildup of toxic nitrogenous compounds, especially ammonia and nitrite. Using a Pond Test Kit to check your water for pH, nitrates, nitrites, alkalinity, and ammonia is important and will help to detect environmental problems that breed disease in your pond. If the water quality is poor you should execute a large (30-50%) partial water change and remove any excess debris. Keeping your water quality high is essential and using TotalPond’s Chlorine Remover gets rid of chlorine and harmful chloramines as well as detoxifies heavy metals that are found in tap water. Also, be sure to have a high quality filtration system like TotalPond’s Complete Filter Kit to maintain quality water. You can attribute sudden losses of fish to low oxygen levels in the water. This can be due to extreme hot weather and over night when oxygen levels decline and plants and fish compete for limited oxygen in the warm water. Ensure your pond has maximum water aeration by keeping aerators, waterfalls, and fountains running at night as well as in the daytime.

A list of preventative measures includes first quarantining new arrivals of fish before adding them to your pond. It may be a pain but new fish may carry pathogens against which your fish may not have strong defenses. This is especially true of goldfish and koi, which are bred in very crowded conditions and shipped from all around the world. Second, keeping low stocks of fish is important because it gives them room to move and limits pathogens from finding hosts to spread disease. Third, set up the pond so the fish have places to hide, rest and sleep. Diseased fish will often segregate themselves, and this behavior alone can reduce the likelihood of transmission. Fourth, keep the water clean and free of pathogens. You can achieve this by keeping the density of fish low which will keep the concentration and variety of pathogens low.

So for healthy fish, maintain high quality water, perform regular pond maintenance, check your fish daily for signs of disease, and your beautiful pond will be ready for your enjoyment.