Golden Freshwater Clam

Parasitic Diseases of Tilapia

Parasites attack tilapia all over the world; in the wild as well as in aquacultures and aquariums. As a tilapia keeper, there are many things you can do to reduce the risk of parasitical attacks and lessen the severity of the attacks that do occur.

Keep your tilapia in a suitable environment

A healthy tilapia kept in optimal conditions will be much less susceptible to parasite attacks. If an infestation still occurs, the fish will be more apt to survive the infestation and handle any treatment. It is therefore important to avoid exposing your fish to factors that will compromise its immune system, e.g. improper water chemistry or sudden environmental changes. Regularly check water parameters such as organic waste (ammonia, nitrite and nitrate), temperature and oxygen content. If you need to change any parameter, e.g. salinity, strive to make the change slow and gradual to give the fish a chance to adapt.

Avoid overcrowding

It might be tempting to fill your growing unit with as much tilapia as possible, but overcrowding will put them at risk for parasite attacks and you might end up loosing a lot of fish. A stocking density that is too high leads to stress which weakens the immune system of the fish and it will also make it easier for parasites to find suitable hosts. Generally speaking, parasites will multiply much more rapidly in a densely stocked growing unit since it is so easy for the offspring to immediately find suitable hosts.

Provide your tilapia with a suitable diet

The immune system of a fish needs a varied and nutritious diet to stay strong. Provide your tilapia with a diet that contains adequate amounts of all necessary nutrients. An unsuitable diet might very well keep your fish alive, but it will weaken their immune system and increase the risk of parasitical problems. Young fish are especially vulnerable to improper diets.

Prevent parasites from spreading

If you have several growing units, it will become important to prevent parasites from spreading back and forth between them. Ideally use separate sets of equipment and do not allow water to overflow from one unit to another.


When tilapia is commercial farmed, it is typically grown in cycles. After each cycle is it advisable to clean out the fish holding system and disinfect all equipment to make sure that no parasites are left from the previous cycle. Parasite populations might otherwise gradually build up from one cycle to the next until they become a serious problem. 

Routine screening

By routinely screening your fish you will learn more about their normal look and habits and increase your chances of detecting parasitical problems at an early stage. Pay special attention to newcomers 

Pay special attention to newcomers

Before introducing a new fish to a growing unit (such as a pond or an aquarium), it is often a good idea to provide it with prophylactic parasite treatment. In some situations it is unadvisable to routinely treat fish that show no symptoms of ill health, but in other situations it is the best course of action since it might save you from having to threat your entire tilapia stock later. If you are hesitant, ask a veterinarian for advice regarding your particular circumstances.

Keep in mind that prophylactic parasite treatment might be necessary not only when receiving fish from outside, but when moving fish from one of your growing units to another as well.

Pay special attention to risky stages

During certain stages of their life, fish are more at risk than normally. You should therefore pay special attention to such fish. Young fish are for instance more sensitive than mature fish, and newly hatched and juvenile tilapia are known to be extremely susceptible to protozoan parasites. Other situations when fish can be at risk are when they are forced to deal with change, e.g. handling and transportation or a change of water chemistry in the growing unit. Seasonal changes can also be a problem, especially if the tilapia is unfamiliar with them from the wild.

Birds and snails

Birds and snails can increase the risk of trematodes such as Clinostomum spp., especially in extensive earthen pond systems. It might therefore be necessary to prevent snails and birds from accessing the growing unit and remove or eradicate the present snail population from the water. Biological control is today available.

Freshwater vs. brackish water

Many parasites have a strict preference when it comes to salinity and can only thrive within a certain salinity range. Some species are for instance found in brackish conditions only, while others can be killed by bathing fish in brackish water. The Amyloodinium spp. dinoflagellates will for instance never occur in freshwater, since they need brackish or marine water to stay alive. The ciliate parasite Ichthyophthirius multifilis can on the other hand be treated with increased salinity since it is adapted to a life in freshwater. As you can see, the salinity level in your growing unit will strongly affect which parasites that you need to look out for. When a parasite attack has been identified, a change of salinity in the growing unit or a short bath might be able to redeem the problem. Always remember that baths and changes in salinity can be hard for your tilapia to handle, especially if already weakened by parasites.

Learn about your strengths and weaknesses

Each culture system has its own weaknesses and strength. As explained above, the salinity of the water will affect which parasites you need to look out for. Salinity is however only one factor among many.

An earthen pond with aquatic vegetation is for instance prone to parasites such as crustacean copepods and leeches since it contains suitable breeding grounds for them. Earthen ponds are also appreciated by animals that acts are intermediate hosts for certain parasites; many digenean trematodes such as Clinostomum spp. will for instance use snails as intermediate hosts.

In addition to earthen ponds, tilapia is often grown in tanks or cages. These cages are rarely inhabited by snails, leeches or crustacean copepods, but they are on the other hand often very densely stocked, a factor which favours the transmission of ectoparasites with a direct life cycle, e.g. monogenean trematodes like Dactyolgyrus spp.

Today, recirculation systems are common due to their many advantages, but build-up of sediment and a slow turn of water can increase the risk of parasitical problem.  Before you decide to keep tilapia in a recirculation system, you should therefore learn more about what you can do to prevent parasitical attacks.  


Many different chemicals can be applied by bath to treat parasites, e.g. organophosphates, hydrogen peroxide, potassium permanganate, formalin and salt. In some situation, ordinary freshwater is the best form of treatment.

Before you use any form of treatment, it is important to identify which parasite you are trying to combat because different parasites require different treatments. Even during prophylactic treatment it is important to take a look at your particular growing unit in order to assess which parasites that could thrive in such an environment. You can read more about common parasitic diseases in tilapia and how to treat them further down in this article.

Your fish
In many situations, the treatment can be almost as dangerous as the parasite itself, especially if you fish is already weakened by illness. You must therefore adapt the treatment to your particular fish in order to avoid killing it together with the parasite. Generally speaking, juvenile tilapia will be more sensitive than mature fish and needs to be treated with special care.

Your growing unit
The type of growing unit will affect which type of treatment that can be recommended. A hobby aquarist that keeps a limited number of tilapia might be able to give each fish a rapid bath, while this would be unmanageable for a major commercial tilapia grower. It is also easy to realise that a large pond will need a different type of treatment than an aquarium. Generally speaking, aquariums and cages can be given short but highly concentrated treatments while ponds and other large growing units typically need to be treated with a low concentration for a long period of time.

In order to make the treatment less risky for your tilapia it is often a good idea to increase the oxygen content of the water. Many commonly used parasitical treatments, e.g. formalin, will decrease the amounts of available oxygen in the water, making it hard for fish to get enough oxygen unless you compensate for the loss by adding extra aeration.

Side effects
As mentioned above, a parasitical treatment can cause unwanted side effects for your tilapia and might even kill it. The tilapia is however not the only one who can suffer. Adding formalin to a pond in order to kill off parasites can for instance result in massive plankton deaths and using sea water to adjust the salinity can introduce new and potentially dangerous organisms to your growing unit. You must therefore carefully assess the risks associated with each treatment before you make a decision.

Legal matters
You must naturally stay clear of any treatment that is unlawful in your particular part of the world.

A Few Examples of Common Parasitic Diseases in Tilapia


Clinostomum spp. (Digenenan)

The risk of Clinostomum spp. problems is highest when tilapia is farmed in ponds that can be accessed by snails and birds.

Symptoms: Clinostomum spp. will normally cause the formation of yellow or white grubs on the skin of the tilapia. In severe case, the parasite can cause skin haemorrhage and death.

Treatment: The best cause of action is normally to prevent snails and birds from accessing the pond and remove or eradicate the present snail population from the water. Biological control is today available.

Dactyolgyrus spp. (Monogenean)

Young tilapia (juvenile and fingerling fish) is especially vulnerable to attacks from these parasites.

Symptoms: Dactyolgyrus spp. can cause darkened skin, eroded fins and excessive mucus production in infested tilapia. Rapid movement of operculum is another common symptom. Young tilapia will often rapidly waste away.

Treatment: Infested tilapia can be given formalin baths or hydrogen peroxide baths.

Argulus sp.

Young tilapia (larval stages and fingerling fish) is especially vulnerable to attacks from this parasite.

Symptoms: Argulus sp. can cause skin irritation and general weakness in infested fish. When the skin is damaged and the fish weakened, it is common for bacteria take advantage of the situation and cause secondary infections.  

Treatment: Argulus sp. infestations can be treated with organophosphates.



Ichthyophthirius multifilis

If you’re an aquarist, you have most likely heard about this parasite before. Among aquarists, the illness caused by the parasite Ichthyophthirius multifilis is referred to as Ich or White Spot Disease. For tilapia, the problem is most severe in larval stages.  

Symptoms: The parasites will cause white cysts to form on the skin of the fish. These cysts look like white spots or small grains of salt. Infected fish will often scratch themselves against rough surfaces in the environment in an effort to rid themselves of the cysts. Ichthyophthirius multifilis can lead to stunted growth and death in tilapia.

Treatment: Many different Ich treatments are available for aquarists, e.g. repeated formalin baths or increased salinity. Some treatments that are practical for hobby aquariums are not feasible for large commercial tilapia cultures.  

Trichodina spp.

Young tilapia is especially vulnerable to Trichodina spp. and this parasite can cause substantial mortality in hatchery and nursery phases.

Symptoms: A tilapia infested with Trichodina spp. can start swimming in an erratic fashion, scrape itself against rough surfaces and jump out of the water. The fins can erode, the gills can develop hyperplasia and skin ulcers can appear. Opened operculum can also be a sign of Trichodina spp.

Treatment: Infested tilapia can be bathed in saltwater, formalin, hydrogen peroxide or potassium permanganate. Many tilapia hatcheries always keep the water salinity in the 5-10 ppt range to prevent protozoan ciliates such as Trichodina spp.



Amyloodinium spp.

These parasites are only found in tilapia living in brackish waters with a salt content of 10-15 ppt, not in freshwater.

Symptoms: A tilapia infested with Amyloodinium spp. will often eat less than normally. Flashing and accumulation of mucus are two other common signs.

Treatment: Since the parasites are adapted to brackish conditions, they can be combated with fresh water baths.


Crustacean copepods

Lernea spp.

Lernea spp. can have a negative effect on mouth breeding in tilapia.

Symptoms: In infested tilapia, it is common to see white spots on the skin. These spots consist of tiny curled up worms that are embedded in the skin. In an effort to get rid of the worms, the fish will often rub itself against rough surfaces in the environment.  

Treatment: Lernea spp. infestations can be treated with organophosphates.




Leeches will normally only be a problem for tilapia fish that is already weakened, e.g. by other parasites, stress or improper environmental conditions.

Symptoms: For adult fish, a severe leech attack with a high number of leaches is normally required before any signs of anemia become noticeable. Young fish are more sensitive.  

Treatment: Leeches can be treated with organophosphates.