Parasitic Diseases of Tilapia
When raising tilapia, there are a lot of things you can do to decrease the risk of parasite problems in your growing unit. The fight against parasites consists of two main parts; the first one is to prevent parasites from entering your growing unit in the first place while the second one consists of keeping your tilapias so strong and healthy that they can fight off parasites instead of succumbing to them. Tilapias also need to be strong to handle any medical treatments because sometimes the cure is almost as dangerous as the parasite itself, especially for a fish already weakened by parasites.
Don’t let them hitchhike
If you have several growing units, don’t let parasites use your equipment to hitchhike from one unit to the next. If possible, use separate sets of equipment for each growing unit or disinfect them before and after each use. Allowing water to overflow from one unit to another is another big risk.
Clean before you restock
Commercially aquacultured tilapia is typically grown in cycles where all new fingerlings are introduced simultaneously and then harvested at the same time. This method gives you the opportunity to clean out your growing units after each harvest to prevent parasite problems. Even if you haven’t noticed any signs of poor health in your current batch, it is a good idea to clean out the growing units nevertheless to prevent parasite build up. If your tilapia was strong, the parasite attacks might have gone undetected. Don’t forget to disinfect all equipment as well. If you farm tilapia in a pond it can be a good idea to let it dry out completely before restocking it.
Birds and snails
Birds and snails can carry parasites, especially trematodes such as Clinostomum spp. Snails and birds are difficult to keep away from earthen ponds, but you can at least decrease their numbers by restricting their access and eradicate the present snail population from the water. Today, biological control is available for tilapia farmers.
A tilapia kept in perfect conditions will have more energy to spend on fighting off parasites than a tilapia kept in suboptimal conditions. It is for instance possible to keep tilapias in temperatures below their natural range, but by doing so you are gradually weakening their immune system of the fish, thus making them more susceptible to parasites.
- Keep the water temperature within the recommended range for your specific species, hybrid or strain of tilapia.
- Regularly check the levels of ammonia, nitrite and nitrate (organic waste) and make sure they are low.
- Regularly check the oxygen content and make sure its high.
- Do not expose your fish to sudden changes, e.g. drops in oxygen or spikes in organic waste. If you need to change something, e.g. the salinity, make the change slow and gradual.
It is naturally tempting to cram a growing unit as full as possible to make ends meet, but doing so can turn out to be a costly mistake since overcrowding makes fish more vulnerable to parasite attacks. An overly high stocking density is stressful for fish and prolonged stress weakens the immune system. The high density also makes it easier for the parasites to spread and virtually all parasite offspring will find a suitable host right away.
Food quality affects the immune system and providing your tilapia with sufficient amounts of all necessary nutrients is important if you wish to prevent parasite outbreaks. As a bonus, a high-quality diet will also make your fish more nutritious. Today, consumer concerns are being raised regarding the low nutritional value of tilapia fish raised on monotonous, low-nutrient diets.
Routine screening will make you learn more about how your fish looks and acts when its healthy and this will make it easier to spot problems at an early stage.
Pay special attention during risky stages
Although tilapias can succumb to parasites throughout their entire life, some stages are more risky than others. Pay special attention to young fish and fish forced to deal with change. Young fish are more vulnerable to parasites than adult fish, and newly hatched tilapia are very prone to attracting protozoan parasites. Regardless of age, change can temporarily weaken your fish and open them up for parasites. Handling, transportation, and changes in water quality or temperature are just a few examples of changes that can be stressful for fish. Seasonal changes can also be a problem, especially if the tilapia is unfamiliar with them from the wild.
Learn about the strengths and weaknesses of your growing unit
Each system has its own strengths and weaknesses and by learning more about them you will be more apt at deciding how to deal with them.
The traditional way of growing tilapia in ponds offers many advantages, but it also makes it difficult to keep parasites away. Earthen ponds with aquatic vegetation are often home to parasites such as crustacean copepods and leeches, and you can also expect your pond to attract animals that serve as intermediate hosts for parasites and can transmit them to your fish. Many digenean trematodes such as Clinostomum spp. will for instance use snails as intermediate hosts, and birds are also known parasite transmitters.
Tanks and cages are much easier to keep free of animals such as snails, birds and leeches, but to make tilapia farming in tanks or cages financially viable the farmers typically stock the growing units very full. This high stocking density favours the transmission of ectoparasites with a direct life cycle, e.g. monogenean trematodes like Dactyolgyrus spp. The stress of living in a densely packed environment will also make the fish less apt at fighting off parasites.
Recirculation systems offer a lot of advantages but build-up of sediment and a slow turn of water can increase the risk of parasite problems. Before investing in a recirculation system, make sure you know how to decrease the risk of parasites in your particular type of system.
Although primarily considered a freshwater fish, some tilapias can adapt to brackish or even marine conditions which gives us the opportunity to grow them in such environments. When raising tilapia in salty conditions you don’t have to worry about strict freshwater parasites such as Ichthyophthirius multifilis since they can’t survive a high salt content. You will on the other hand open up for an entire new set of parasites, such as the Amyloodinium spp. dinoflagellates that only lives in brackish in marine waters. As you can see, the salinity level will strongly affect which parasites that you need to look out for in your tilapia farm.
Tilapia parasite treatments
There are many different treatments available and the safest course of action is to consult a veterinarian to get a proper identification of the culprit and treatment suggestions adapted for your particular growing unit. The sooner you notice the parasite attack and contact a veterinarian the better, because tilapia fish already weakened by prolonged parasite infestation can have a hard time surviving the treatment.
To combat parasites in tilapia, various chemicals can be applied by bath, such as organophosphates, hydrogen peroxide, potassium permanganate, formalin, and salt. Many parasites can be killed using ordinary saltwater baths or freshwater baths, depending on the preferences of the specific species of parasite, but in some situations you need stronger remedies. It is also possible to your medicated food, provided that your tilapias are still eating.
Identify your foe
Different parasites are vulnerable to different treatments so it is important to identify the culprit before you commence treatment. It might not be possible to pin down the exact species, but you can at least determine which type of parasite it is.
How strong is your fish?
As mentioned above, parasite treatment can be almost as stressful as the parasite itself so it is important to assess the condition of your tilapia before you commence treatment. For fish already weakened by parasites, the treatment can be the final straw that breaks the camels back. Generally speaking, juvenile tilapias are more sensitive to treatment than adult fish and it is more difficult for them to survive treatment.
How will you administer treatment?
Which type of growing unit you are using will affect how treatment can be administered and this will in turn affect which type of treatment that can be recommended. If you were a hobby aquarist with ten sick guppies you may be able to give each fish a rapid bath, but such solutions are rarely a feasible alternative for tilapia farmers. Generally speaking, tilapias living in tanks or cages can be given short but highly concentrated treatments while pond tilapias need to be treated with a low concentration of the active substance for a long period of time.
Increase the aeration
Sick fish often find it difficult to breathe, especially if their gills have been infested with parasites, and it is also common for them to consume more oxygen than normal– a very bad combination. To make things even worse, many commonly used parasitical treatments, e.g. formalin, will decrease the amounts of available oxygen in the water. By boosting aeration in the growing unit you will make the environment much more beneficial for your tilapia fish and increase their chances of survival.
The tilapia fish and their parasites are not the only ones affected by treatment and the long term effects can be hard to predict. Adding formalin to a pond can for instance kill off massive amounts of plankton which in turn can lead to a scarcity of both food and oxygen; a scarcity that you will be forced to compensate for if you want your tilapia to thrive. Using sea water to increase salinity will often kill off all the freshwater parasites, but you will on the other hand subject your fish to a whole new range of marine parasites. As you can see, it’s important to assess the risks associated with each treatment before deciding which treatment to use.
Always check up current regulations applicable to your area to prevent getting into legal trouble. Just because a remedy was legal last time you used it doesn’t mean that it is legal today. Also keep in mind that you might need some type of license. And as the saying goes; a 2$ license is better than a 200$ fine.
A Few Examples of Common Parasitic Diseases in Tilapia
Clinostomum spp. (Digenenan)
Clinostomum spp. is more common in ponds than in cages and tanks, since it is spread by birds and snails. Restricting wildlife access to the pond and eradicating the current snail population will decrease the risk. Biological snail control is today available. Symptoms of Clinostomum spp. include yellow or white grubs appearing on the skin of the fish. In severe cases, skin haemorrhage will occur and deaths are not uncommon.
Dactyolgyrus spp. (Monogenean)
These parasites are especially dangerous for fingerlings and juvenile tilapia, who are known to rapidly waste away once they have become infested. Symptoms include darkended skin, fin erosion, excessive mucus production, and rapid movement of operculum. The parasite can be killed using formalin or hydrogen peroxide baths.
Just like Dactyolgyrus spp., the Argulus sp. parasites are especially dangerous for young fish. Larval stages and fingerlings are especially at risk and secondary infections often kill them once the parasite has weakened them sufficiently. Symptoms of Argulus sp. includes irritated and damaged skin, and the fish typically become weak and listless. Argulus sp. can be killed with organophosphates.
Ichthyophthirius multifilis, commonly known as ich or white spot disease, is a common parasite in freshwater aquariums and it can infest tilapia grown in freshwater as well. Outbreaks are especially common in growing units containing larval stages and the parasite can lead to stunted growth or even death in tilapia. As you may have guessed from the name whit spot disease, infested fish become covered in white spots. The white spots look like tiny grains of salt and are cysts filled with parasite offspring. In an effort to rid themselves of the parasites, infested tilapia can often be seen scratching their bodies against rough surfaces in the growing unit. Many different treatments exist for ich and repeated formalin baths or increased salinity are just two examples of methods known to eventually kill off ich. You have to be persistent since ich parasites are quite resilient during certain stages of their life cycle. Quite a few of the available ich treatments have been developed for aquariums and may not be practical for large tilapia units.
Trichodina spp. is known to cause significant mortality in hatchery and nursery phases. Adult tilapia is usually more resilient. Symptoms include erratic swimming, eroded fins, skin ulcers, opened operculum, and hyperplasia of the fins. You may see the fish trying to jump out of the water and the skin irritations can make it scratch itself against rough surfaces in the growing unit. Trichodina spp. is sensitive to formalin, potassium permanganate, hydrogen peroxide, and ordinary saltwater. It is quite common to keep the salinity at 5-10 ppt in tilapia hatcheries to protect the young ones against freshwater protozoan ciliates such as Trichodina spp.
Amyloodinium spp. are not a problem in freshwater units but can occur in brackish units where the salinity is 10-15 ppt. Symptoms include loss of appetite, flashing, and accumulation of mucus. The parasites can be fought off using freshwater baths since they require brackish conditions.
Lernea spp. is especially dangerous for mouth breeding tilapias. The most visible symptom is white spots on the skin; white spots that are actually tiny curled up worms embedded in the tissue. Infested fish can often be seen scratching their skin against rough surfaces in the growing unit. Lernea spp. is sensitive to organophosphates.
Adult tilapias are normally quite resistant to leeches, but if the fish is weakened by something else leeches can become a serious problem. Stress, health problems, and improper environmental conditions are all examples of things that can leave your tilapia open to massive leech infestations. When a high number of leeches draw blood from a fish it can lead to anaemia. Young tilapia fish are more sensitive than adults. Leeches can be combated using organophosphates, but if you don’t do anything about the underlying cause they – or some other parasite – will most likely deliver a new blow to your tilapia population within short.