Do You Know the Signs, Symptoms & Treatments for These Common Fish Illnesses?

Date Posted:21 October 2022 


Can fish get sick? They might not be as obvious about it as other animals, but fish can become ill all the same. If you are new to owning fish, it can be difficult to recognise symptoms as they come up, and this makes it all the more stressful to care for your beloved pets. Fortunately, there is plenty of information out there to guide you, and many ways to prevent and treat diseases affecting fish.


Fish can contract bacterial, fungal, parasitic and viral diseases, so can benefit from various kinds of specific treatment. Generally speaking, if you regularly perform aquarium maintenance and keep fish medicine in handy, you can feel confident that any illnesses may occur can be dealt with swiftly and effectively.


What to Do When Fish Are Sick


If you suspect that something is wrong with your fish, take the time to observe them closely and determine what exact illness they are likely to have. This is important because, as a general rule, there are specific fish medications to treat each type of fish disease. That being said, Broad Spectrum Fish Medication is one of the best fish medications to have on hand, as it deals with bacterial, fungal and parasitic diseases.


How to Tell If Your Fish Are Sick


Symptoms vary from illness to illness, but there are some overarching signs to look out for. It is helpful to familiarise yourself with these signs so that you can spot symptoms as soon as they occur, administer treatment right away, and thereby minimise any discomfort for your fish. Common signs of fish disease include lethargy (slowed swimming), itchiness or irritation (as indicated by rubbing themselves against objects), and various forms of disfigurement or discolouration.


Which Bacterial Diseases Should You Watch Out For?


While bacterial diseases can be quite aggressive, most of them are perfectly treatable — especially in the early stages. This is because bacterial fish medication is available to alleviate symptoms and, in the majority of cases, eradicate diseases. If you require fish care products for betta fish specifically, you can even find Bettafix antibacterial medication. Betta water conditioner also exists, so you can improve the quality of your aquarium’s water without stressing over whether your bettas can withstand the adjustment. Many bacterial diseases are triggered or exacerbated by poor water conditions, so a tool such as this can be incredibly helpful.


Cloudy Eye


Cloudy eye is one of the most common diseases among freshwater fish. The effects can be quite serious, with some fish experiencing a loss of vision. Other symptoms include the appearance of white cloudiness across the eyes, as well as erratic swimming. This disease can be caused by poor diet, a parasitic or bacterial infection, poor water quality, or even something as simple as old age.


If you suspect that your fish may be suffering from this disease, begin treatment by testing the pH of your water. If it is lower than 6, raise it using crushed coral or marine salt. You should also perform water changes, add some water treatments and continue to monitor the water and your fish going forward.


Columnaris (Mouth Fungus)


While this disease is known as mouth fungus, it actually also affects the body and gills. You may see ulcers appear on the body, as well as cloudy, fungus-like patches on the body, gills or mouth. If your fish has columnaris, it might experience a loss of appetite, difficulty breathing and, eventually, rotting of the gills or mouth. Columnaris is born from a highly contagious bacteria that can affect all fish, but it can be contracted as a result of poor diet, bad water conditions, overcrowding or anything that triggers stress in your fish.


To treat, add aquarium salt and antibacterials to the water. You should also check your tank water parameters and make changes as necessary.


Fin or Tail Rot


If you notice white marks, fading or other signs of decay at the ends of your fish’s fins or tail, your fish might have fin or tail rot. Other symptoms include difficulty swimming or spending more time at the bottom of the tank than usual. Fin rot can be caused by several bacterial species, but housing your fish with incompatible tankmates is often the primary reason for this disease’s occurrence. Any fin nipping by aggressive fish can lead to a bacterial infection, as can the stress-inducing overcrowding of a tank.


To fix this problem, improve your water quality by completing a 25 to 50% water change and syphon your gravel. If your tank is overcrowded, find new homes for some of your fish — particularly the fin-nippers. You can then administer antibacterial medications.


Learn How to Spot These Fungal Diseases


Given the opportunity, fungi will invade most organic material, including live tissue. This is why you need to ensure that your fish tank is clean and that conditions are appropriate to house your fish.


Body Fungus


If your fish has suffered any damage to its skin or has any open wounds, it might be vulnerable to body fungus. Keep an eye out for white, brown or green cotton-like strands growing from the head, body or fins, as well as general discolouration of the body. Your fish might also display signs of lethargy, such as slow swimming, or possibly even erratic movements. If your fish is under particular stress, such as that caused by temperature changes or poor water conditions, it will be more likely to develop body fungus. Essentially, the mucus layer on your fish’s skin should stop the fungal spores from taking hold so long as your fish are healthy.


If you do get an outbreak, however, it should be okay as long as you work quickly. Treat the body fungus with fish antifungal medicine such as fungus and fin rot medication.


Cotton Fin Fungus


This fungus appears as very white, cotton wool-like growths on the fins, while the dead tissue beneath the growth might show signs of rot. The fish may swim slowly, erratically or in a way that allows them to scratch themselves against objects in the tank. Cotton fin fungus is caused by an excess of food or rotting material left in the tank, which will inevitably lead to poor water quality. Older fish or those with weakened immune systems will also be more likely to experience cotton fin fungus.


Fish anti-fungal medicine exists to help fight this fungus, but in many cases it can go away on its own once the water quality of the tank improves.


Parasites Can Post a Real Risk


There are many types of internal and external parasites that can impact the health of your fish. Fortunately, parasite medication for fish is highly effective and easy to administer. So, how do you treat a sick fish? Since these particular medications tend to come in the form of capsules, all you need to do is pre-dissolve them in a disposable cup and add them to the aquarium.


It should also be noted that parasitic diseases can be triggered by stress, which lowers the fish’s immune systems and leaves them vulnerable. Stress might occur as a result of poor water conditions, temperature changes and an overcrowded tank, so make sure to have all the supplies necessary for fish tank maintenance at your disposal.


Anchor Worms


Anchor worms are large parasitic crustaceans that can attach themselves to a fish’s skin and bury their head into the muscles. If you see your fish rubbing their body against the tank, or notice that their scales are red and inflamed, they might have anchor worms. If you look closely, you might even be able to see the body of the parasite sticking out of your fish. This would look similar to small, whitish-green threads.


To treat this ailment, carefully remove the parasites by pulling on their bodies, and then apply an antibiotic ointment on the scales. You can then clean the tank to get rid of eggs, larvae and parasites.


Ich (White Spot)


Ich is one of the most common parasitic diseases you’ll find in aquariums, largely because it is extremely contagious. This disease is often contracted as a result of high stress levels in the fish. If your fish has ich, you may notice small, raised, circular white spots spread evenly across the gills and body (rather than appearing in clusters). To fight off irritation, your fish might scratch itself against objects. It could also frequent the surface of the tank to gasp for air, or clamped fins.


Before you diagnose your fish, it is important that you determine whether their spots appear spaced out or in clusters. If the spots are bunched together and don’t appear to be raised, your fish might be suffering from a different illness, such as epistylis.


Once you’re confident that your fish has ich, use a white spot parasite medication for around 14 days. This should be enough time to remove all parasites and carrier cysts from the fish and their environment.


Velvet Disease


Also known as gold dust disease, the symptoms for velvet disease include the appearance of small gold or rust-coloured dust-like specks on the head and body. The fish may also have clamped fins, laboured breathing and a lack of appetite, which will lead to weight loss. If you notice that your fish seems lethargic or is rubbing itself up against objects, this could also indicate that something is wrong. Velvet disease can affect both freshwater and saltwater fish, and is often the result of stress.


It is quite common and can be serious, so make sure to treat it as soon as you can with a copper-based medication. Other treatments include keeping the aquarium in darkness or raising its temperature to around 27°C — although you should double-check that your species of fish can withstand these temperatures beforehand.


Fish Lice


Fish lice, or argulus, are among the largest parasites affecting marine and freshwater fish. They can sometimes even be visible, appearing as tiny dark oval lice around the fish’s head or pectoral fins. You may notice inflamed areas where the lice are attached, and the fish might attempt to rub themselves against objects for relief. Your fish might also start to swim erratically, darting around the aquarium.


To treat, carefully remove the lice from your fish’s body with tweezers and administer a diflubenzuron-based medication. Fish lice can be introduced to your aquarium via infected fish, which is why it’s so crucial to properly quarantine new friends before you add them to your tank.


Be Aware of Viral Fish Diseases Too


As we’ve already established, it can be hard to tell if fish are sick. Sometimes, fish that appear perfectly healthy are added to a tank only to spread viral diseases among the original school. This is why it is so important to complete a proper quarantining process before you add new fish to your tank.


Thankfully, it is pretty easy to alleviate the impacts of viral fish diseases via regular fish tank maintenance. If you are keeping your water conditions monitored, ensuring effective aquarium filtration and refraining from overcrowding your tank, your fish should recover fairly quickly. You can also improve your water conditions by adding aquarium water treatment.




Lymphocystis is a common viral infection that affects fresh and saltwater fish. It is not usually too serious, disfiguring the skin and fins but very rarely resulting in death. This virus causes cauliflower-shaped, cotton-like patches to appear on the head and body, as well as white patches around the eyes. Fish can become lethargic, and start swimming slowly or erratically. If several growths are on the gills, they might experience difficulty breathing.


Aquarium fish stress relief medications such as Aquarium Salt are great to use in this case, as they can improve gill function and make it easier for fish to breathe. However, there are currently no fish medicines available that directly treat this fish disease. In most cases, infected fish are able to fight the virus off within a month, but you can certainly aid this process by treating the tank with a general cure.


Where Can You Buy Fish Medicine?


Caring for fish can be stressful, but everything is easier with the right advice and products. If you need fish medicine, trust the home aquarium experts at Aquarium Kingdom. Our enthusiastic team prioritises the health and happiness of your fish, and are always happy to answer any questions you have about fish care. For high-quality fish supplies and medications, visit the Aquarium Kingdom website now!


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