The guide will give you tips on how to spot and cure different diseases that freshwater fish often get. However, it’s always best to consult a vet.
And remember that some of these treatments can harm live plants and certain types of fish like some catfish and other tropical fish that are more fragile or sensitive.
If you have a fish that’s sick, it’s best to treat them in a separate tank, away from the other fish.
With that said, here are the 19 most common freshwater aquarium fish diseases and their cures.
Fin Rot
Fin rot is a common disease that can harm your fish’s fins. If your fish’s fins look torn, ragged, or like they’re falling apart, it might be suffering from fin rot.
The fins might also look red or swollen. It may seem as if your fish has swum through a fan.
Fin rot is caused by harmful bacteria that can spread easily from one fish to another. These bacteria are usually present in water that isn’t clean.
Also, if your fish gets injured, it’s more likely to get fin rot. Sometimes, this disease can lead to a fungal infection.
To heal fin rot, you can apply gentian violet, a type of medicine, directly to the affected areas. You can also add a medicine called SeaChem Kanaplex to the water.
Add one tablespoon of aquarium or marine salt for every five gallons of water.
While you’re treating your fish, make sure to remove any activated carbon from filters.
Also, frequently change the water to keep it clean.
All these steps can help improve conditions and help in the recovery of your fish from fin rot.
Dropsy
If your fish has a swollen body, scales sticking out, and looks like it’s been stuck with pins, it may have dropsy.
This disease can be caused by a few different things, such as organ failure due to cancer or old age, a bacterial infection, or poor quality water.
To treat dropsy, you should first fix any issues with the water conditions. Once that’s done, use a bacterial treatment called API Melafix.
But keep in mind that if the disease is caused by organ failure or cancer, there’s no cure.
You can also try changing the water frequently to improve its quality. This might make your fish feel a bit better.
However, it’s important to note that it’s not very common for a fish to fully recover from dropsy.
Freshwater Ich
Freshwater ich is a fish disease that you can identify by the sudden appearance of small white spots on the fish’s body and fins. These spots resemble tiny grains of salt.
In the later stages of the disease, the infected fish will continually scratch themselves on the tank’s gravel and decorations.
If you notice your fish behaving as if they’re rubbing against the rocks in the tank, they likely have ich.
The cause of this disease is a parasite called Ichthyopthirius. This parasite lives on the host fish, and when it’s mature, it falls off and multiplies in the tank’s substrate.
After multiplying, the new parasites then look for another host to infect.
To treat ich, you can use a specific ich remedy, which often contains formalin or malachite green.
Even if you move the sick fish to a separate tank, you should still treat the water in the main tank with medication. This will eliminate any remaining parasites that are still swimming freely in the water.
When using formalin, always wear gloves to protect your skin.
Swim Bladder Disease
Swim bladder disease is a common fish disease. It affects the organ in a fish that helps it to float and balance in the water.
If your fish has this disease, you might notice them swimming in a strange way. They might look like they’re doing a doggie paddle but upside down, or they might seem to lose their balance completely.
This disease can be caused by different things. It might be due to bacteria infecting the fish.
It could also happen if the fish gets hurt. This could be from fighting with other fish, when they’re breeding, when you’re moving them with a net, or even when they’re being transported from the shop.
Another cause of this disease is poor water quality.
If your fish has swim bladder disease, you can treat it with antibiotics. It’s best to do this in a clean tank with shallow water.
The water should be just deep enough to cover the fish – about 2 inches above its top fin. Also, try to change the water often – every day if you can. This will help keep the water clean and help your fish get better.
Freshwater Velvet
Freshwater velvet is especially common among species like bettas. It’s named so because it causes a golden or grayish-white coating on the fish’s body or fins.
If your fish has this disease, it might look like it’s covered in gold dust.
This disease is caused by a parasite called Piscinoodinium. These adult parasites latch onto your fish’s skin.
After about a week, they fall off, drop into the gravel or sand at the bottom of your tank, and start multiplying.
The new parasites then get released into the water and swim around searching for a new fish to infect. If they can’t find a new host within two to three days, they die off.
To treat freshwater velvet, use a special remedy that contains malachite green. You should also add a tablespoon of aquarium salt to every 5 gallons of water in your tank. This will help your fish fight off this disease.
Constipation
Constipation in fish is a common illness. It’s often seen when a fish isn’t eating much or at all.
If you notice that your fish hasn’t produced any waste or its stomach looks bloated, or if it’s not moving around much, it might be constipated.
Also, if your fish hasn’t left its bottom dwelling for over a month, it could be a sign of constipation.
The main causes of this are improper feeding or giving them too much food. To treat this, you can add a little bit of magnesium sulfate, about a teaspoonful for every two gallons of water in your fish tank.
Another thing you should do is stop feeding your fish for a few days.
After this, make sure to improve your fish’s diet. Try to feed them live foods more often.
Hole In The Head
Hole in the head is pretty common, especially in cichlids. The main sign of this disease is if you see the fish have holes on their head, close to the line on their side or near their tail, which are filled with pus.
This disease is caused by a troublesome little parasite called Hexamita.
But don’t worry, there’s a treatment for it. The medicine you need is called Flagyl. Recent research has also found that giving the fish vitamin supplements, particularly Vitamin A and C, can help them get better.
Remember that these should be vitamins specifically made for water animals.
So, watch out for these symptoms and act fast if you see them. It’s not too hard to treat if caught early.
Pop-eye
Pop-eye is a fish disease where the fish’s eyes get inflamed and stick out almost as if they’re about to pop out. The eyes may also turn cloudy and white. The area around the eyes can also get swollen.
This usually happens because of parasites or if the fish is living in dirty water.
Unfortunately, there’s no ready-made medicine you can buy to treat this. The best thing you can do is keep the water in the fish tank clean by changing it regularly.
Also, test the water for things like pH, ammonia, nitrites, and nitrates, and make sure they’re at the right levels.
Another good idea is to add a tablespoon of aquarium salt for every 5 gallons of water in the tank. This can help control the balance of water and salts in the fish’s blood.
Fungus
Fungus is a common problem that you might see in your aquarium. You can tell your fish might have this disease if it starts to develop fluffy, white patches on its body or fins.
It can make your fish look like it’s covered in cotton or marshmallow fluff.
The reason this happens is because of the fish’s mucus or slime coating getting damaged. This might be due to an injury or being attacked by parasites.
Once the slime coating is gone, the fish is open to all sorts of other diseases.
To treat this, you can use gentian violet or methylene blue, which you can just dab onto the affected areas. If things get really bad, you might need to use an aquarium fungicide.
Mouth Fungus
Mouth fungus can be tricky to understand, especially if you’re new to this. So, let’s break it down.
Imagine your fish looking like Santa Claus with a messy beard. That’s what mouth fungus looks like.
It’s a white, cotton-like growth around the fish’s mouth or a patchy white area on its skin. If it gets worse, the fish’s jawbones start to break down.
It’s usually caused by a bacteria called Flexibacter. But, this usually only happens after the fish has already had another infection.
There are special fungus treatments you can buy or a blue dye called methylene blue that can help in the early stages of the disease.
But, if these don’t work and the fungus gets worse, you should talk to a vet about getting antibiotics right away.
Bacterial Infection
Bacterial infection is caused by Aeromonas hydrophila. This bacteria can cause your fish to develop symptoms like blood spots, open sores, ulcers, and frayed fins.
If you notice any of these signs, it’s important to treat the infection quickly to help your fish get better.
One popular treatment is a product called API Melafix. It’s a kind of medicine for fish that can help fight off the bacteria causing the infection.
Just like humans take medicine when they’re sick, it’s important to give fish the right treatment when they’re not feeling well. This will help them recover and stay healthy.
Gill Parasites
Fish disease caused by gill parasites (also known as Flukes or scientifically, Dactylogyrus) is a common issue in the aquatic world.
If your fish are showing signs like redness around their gills, difficulty in breathing, rubbing their body against surfaces, excessive slime, hazy eyes, inflamed gills, or unusual, wild movements (kind of like they’re at a punk rock concert), they might be dealing with this disease.
But don’t worry, there are ways to treat it. You can use products like Sterazin or Praziquantel, which are specially made to fight against these parasites.
Another helpful treatment can be giving your fish a bath in a solution containing formalin. To be effective, make sure to follow the instructions provided by the manufacturer of these treatments.
Intestinal Parasites
Intestinal parasites in fish are a type of disease that can be caused by various types of worms living in the stomach and intestines.
You might notice this issue if you see worms hanging out from the fish’s bottom part, or if the fish becomes really thin.
These parasites can be treated in a few ways. The first way is to use a standard fungus medicine that you can buy in most pet stores.
If the problem is really serious, you might need to use a stronger medicine like API General Cure, or a worm-killing medicine that a vet can give you. This medicine should be added to the fish’s food every day.
Another thing you can do is adding a tablespoon of aquarium salt for every 5 gallons of water in your fish tank. This can help your fish’s body work properly.
If you have activated carbon in your tank, you should take it out while you are giving the fish medicine.
Also, you should change about 15 percent of the water in your tank every day. This can help keep the water clean and healthy for your fish.
Large Skin Parasites
Large skin parasites is a common problem that can affect your pet fish. The main culprits behind this issue are usually fish lice and anchor worms. These pests latch onto the fish’s skin and cause discomfort and distress.
When your fish is infected with these parasites, you might notice them scratching against surfaces more often. This is an attempt to get rid of the irritating pests.
Also, if you look closely, you might be able to see the parasites themselves on your fish’s skin.
Treating this disease is a two-step process. Firstly, you’d need to physically remove the parasites. This can be done using a pair of tweezers. Be careful not to hurt your fish in the process.
After you’ve removed the parasites, the second step is to apply an antiseptic solution to the areas where the parasites were attached. This helps to prevent any infections and helps in the healing process.
Tuberculosis (TB)
Fish tuberculosis, often just called fish TB, is a severe sickness that can affect your pet fish.
Fish who have TB may appear to lose color and become pale. Their fins might look damaged or be tightly clamped together.
These sick fish often lose a lot of weight quickly, and might have sores or ulcers on their body. They could also develop pop-eye, where the eye bulges out.
Fish TB is caused by bacteria, most likely due to poor water quality in the tank or if the tank is too crowded.
It’s important to know that this disease can sometimes be passed to humans if they touch the infected areas on the fish.
If you think your fish might have TB, you should be very careful. Many people believe it’s too risky to try and treat the fish because it could put you or your family’s health in danger.
If you need to handle the fish, make sure you wear plastic gloves.
The best thing to do for a fish with TB is to euthanize it right away. If an infected fish is left in the tank, other fish might eat it and then they could get sick too.
Skin Flukes
You can tell your fish might have skin flukes if their skin looks red and inflamed, if they have a lot of mucus on their skin (it would look like they’re covered in a thick, slimy substance, kind of like Vaseline), or if they’re scratching themselves a lot.
This disease is caused by something called Gyrodactylus salaris. This is a kind of parasite that attaches itself to the skin of the fish and causes the disease.
You can get a special kind of medicine that’s made just to treat this disease. One example is Hakari PraziPro.
Make sure to look at the label and see if it says it’s for treating skin flukes. That’s how you’ll know it’s the right kind of medicine.
Slimy Skin Disease
If you notice that your fish has a grayish slime on its body or fins, it might be suffering from a condition known as slimy skin disease.
Other signs to look out for include the fish scratching itself, its fins looking ragged, producing too much mucus, and moving in a shaky manner, similar to a politician avoiding difficult questions.
This condition is caused by tiny parasites called Costia, Trichodina, Cyclochaeta, or Chilodonella.
You can use a special remedy that contains malachite green to treat this disease. Additionally, you should change the water in your fish tank frequently.
For an immediate relief, you can give your fish a quick (about 5 minutes) bath in a solution of formalin and salt.
Also, make sure to check the water conditions in your tank and correct them if necessary, because poor water quality can contribute to this problem.
Fish Louse
Fish louse is caused by a small creature, like a tiny crab, that sticks to the fish’s skin. The louse is round, and because it feeds on the fish’s skin, it often leaves sores. These sores can then become infected with bacteria or fungus.
The louse is a type of creature that can leave its host, the fish, and lay eggs. These eggs are enclosed in a jelly-like substance and are often found on the bottom of the tank or on the decorations in the tank.
The eggs may not hatch until the water in the tank gets warmer, and they can stay in the tank for a long time.
The way to treat a fish who has the louse sickness is to remove the louse from the fish. This can be done with a small tool like tweezers.
If there are any sores on the fish, you can clean them with a cotton swab that has been dipped in a special type of medicine called Mercuro-chrome.
The last step is to clean the tank. This means taking out the water and cleaning all the decorations and the bottom of the tank. Basically, you need to start fresh.
Septicemia
Septicemia is a pretty serious fish disease. If your fish gets this disease, you’ll first notice some redness near the bottom of their fins. This will be followed by lines that look like blood appearing on their fins and body.
Other signs that your fish has Septicemia include bleeding, not wanting to eat, and being sluggish. This disease often comes after fin rot or skin infections.
If it gets worse, it can cause serious damage to the fish’s heart and blood vessels. This leads to leakage of fluid in their belly, which can sometimes cause dropsy.
This disease is caused by bacteria called Pseudomonas or Streptococcus. These bacteria cause inflammation in the body tissues of the fish. This usually happens if the fish already has a skin infection.
To treat Septicemia, you can use antibacterial medicines like Furan2 or Triple Sulfa. Also, remember to change the water in the fish tank every one to one and a half days.
