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Tips For Treating And Preventing Parasitic Infections In Freshwater Tropical Fish

Tropical fish are potential hosts to a variety of parasites. In this article you'll learn about common parasite infections that affect tropical fish and get valuable tips for prevention and treatment.


molly giant-sailfin xs 8281498Parasites can be found in almost all groups of plants and animals – aquarium fish are no exception. These organisms are capable of causing a variety of harmful infections which can result in skin lesions or growths, difficulty breathing and eventual death. In order to protect your fish from deadly parasite infections, it is wise to cultivate a basic understanding of parasites and the common diseases to which your fish may become exposed. Once you have learned the basics about these infections, you will be better equipped to identify them and to take action if one of your fish falls ill. Quick action on your part, as the aquarium hobbyist, can mean the difference between a fish successfully recovering because it received prompt treatment and the fish dying because its condition was diagnosed too late.

What Are Parasites?

parasites xs 10021752A parasite is an organism which invades the body of another organism and feeds on it. In many cases, the parasite benefits at the expense of the host body which may decline in health and could even be killed as a result of the infection. Parasites are typically divided into two groups: ectoparasites and endoparasites. Ectoparasites are those parasites which live on the outside of the host body, namely the gills, mouth, fins and skin of aquarium fish. Endoparasites are those which live inside the host body, inhabiting the blood, tissues and/or organs. Parasites can be transmitted through a variety of means depending on the particular parasite. Some are transferred through direct contact while others, in the free-living phase, can be found floating in tank water or inhabiting the substrate. Parasites having a direct life-cycle are transmitted directly but may involve a free-living phase where they can survive in tank water for a limited period of time. Parasites with an indirect life-cycle can only survive in the host body.

Common Parasite Infections

Trichodina – Though there are technically three genera which form the Trichodina complex, all three parasites are referred to using the same name - Trichodina. These parasites typically affect the gills of fish, causing the infected fish to experience respiratory difficulties and erratic behaviors such as piping and flashing. Cutaneous Trichodina infections, those affecting the skin, may cause ulceration or erosion of the fins. As the infection progresses, affected fish may become lethargic and could also lose their appetite and isolate themselves from other fish. Common treatments for this infection include potassium permanganate and salt baths.

Ichthyophthirius multifilis – Perhaps the most common parasite seen in tropical fish, Ichthyophthirius multifilis is more commonly known as Ich or White Spot Disease. This disease is caused by the protozoa Ichtyopthirius which is an ectoparasite, meaning it lives on the outside of the host body. These parasites can grow up to 1mm in length and look like small white spots that appear on the body, fins and gills of infected fishes. Each of these spots is a parasite in cyst form – inside each cyst, the parasite rapidly multiplies and can then be spread to other fish in the tank. Because this disease is highly contagious and resilient, it is often recommended that you treat the entire tank rather than quarantine infected fishes. The most common treatment for this condition is a salt bath to kill the parasite, though chemical treatments such as formalin, malachite green and copper sulfate are also effective.

Ichthyobodo – Also known as Costia, this disease is caused by protozoan parasites. Though it is not one of the most common parasite infections, it is relatively easy to cure. This infection typically presents in the form of cloudy or milky skin as a result of excessive mucus production and it may also cause ulceration and erosion of the fins. Raising the temperature in the infected tank to 83° Fahrenheit may help to kill the parasite but it may not be effective against serious outbreaks. Acriflavine and other medications containing copper are generally more effective, but both of these substances can be harmful to fish in large doses so exercise caution when using either of these treatments.

Hexamita – Once thought to be responsible for lateral line erosion, or hole-in-the-head disease, the Hexamita parasite is poorly understood. These parasites typically infect the gastrointestinal tract of aquarium fish, causing symptoms similar in appearance to those induced by malnutrition. One of the first symptoms likely to occur in infected fish is slimy white feces. As the disease progresses, more severe symptoms including difficulty swimming, weight loss and skin darkening may be observed. The most common treatment for this parasite is a 1% solution of metronidazole in fish food.

Chilodonella – This disease is caused by a protozoan parasite and it can be very difficult to diagnose. The Chilodonella parasite typically enters the tank through infected fish/decorations or through contaminated live food. The most common symptoms of this disease include rapid breathing, excessive mucus secretion, loss of appetite, clamped fins and rubbing against tank objects. When first infected, fish may exhibit no signs of illness – once symptoms are seen, the disease could be in the final stages. Popular treatments for Chilodonella include salt baths as well as commercial medications such as formalin, malachite green and potassium permanganate.

Tips for Treating and Preventing Parasites

parasite xs 2325761When it comes to treating a parasite infestation, you need to first decide whether you want to treat the individual fish or the entire tank. If you catch the parasite early enough that only one of your fish has been infected, removing that fish to a quarantine tank for treatment may be sufficient. Even if only one of your fish seems to be infected, however, treating the entire tank is a wise precaution. Just remember to remove any carbon filter media when treating the tank as carbon will reduce or negate the effectiveness of medications. Before you make this decision it may be helpful to identify the type of parasite involved – some parasites are unable to survive in tank water, so treating the entire tank may not be necessary.

As is true in regards to all types of freshwater fish diseases, parasite infestations are more likely to affect fish which are already stressed due to poor water quality or other factors such as bullying, injury or prior illness. In order to give your fish the best chance possible in fighting off a parasite infection it is wise to perform regular water changes and to install a high quality aquarium filter in your tank to keep the water clean. Feeding a well-balanced diet of live, frozen and freeze-dried foods as well as commercial foods such as flakes and pellets is also important in keeping tropical fish healthy. Fish that are fed a healthy diet tend to be less susceptible to disease and, in the event that they contract a parasite infection, they may be more likely to recover successfully.

The most important, and perhaps the most basic, step you can take in preventing parasite infections among your freshwater tropical fish is to quarantine all new fish before adding them to your aquarium. It can be difficult to tell just by looking at a fish whether it carries parasites or is currently suffering from an infestation, so quarantining the fish is the safest option. New fish should be kept in quarantine for at least two weeks before being added to the main tank. During this period, observe the fish for signs of illness and start a treatment regimen if necessary. If, after the two week period has passed, the fish show no signs of illness – or they have recovered fully from an illness you treated – they can be safely added to the main tank.

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