Information, Freshwater fish, Saltwater fish

Common Fish Diseases (Treatment and Symptoms)

Photo of author

by Jason Matthews



Fish, like other animal species, are susceptible to diseases. If you are new to the aquarium field, you need to be well informed about the common fish diseases, their symptoms, and treatment methods.

Your fish’s well-being can be affected by slight environmental changes in the fish tank, which trigger stress. The most common reasons fish get sick are parasitic, bacterial, fungal, and viral infections.

Once you notice something wrong with your fish, you need to figure out what could be the problem. If you are aware of the common diseases that affect fish, you could conduct some easy home treatments. However, if the issue persists, you can talk to the aquarium store for details about how to treat them.

Here are some of the common fish diseases and how to treat them. 

Common Parasitic Infections

Hole in the Head

This disease is caused by a parasite known as Hexamitosis. It affects both freshwater and saltwater species.

A hole in the head can also be due to poor quality food and issues with the water conditions. In addition, your fish can get affected by this condition due to a deficiency of minerals in the water, especially if you use excess activated carbon for your filter.

It’s a common disease among Cichlids.


  • Small indentations around the head
  • Ulcers along the lateral line
  • Fish losing color
  • Fish stop eating


If you spot the symptoms early enough, you can treat hole in the head before it becomes too severe. The best way to treat this condition is by isolating the fish in a separate quarantine tank. Additionally, you could also treat the issue using metronidazole.

Ich or White Spot

Ichtyophthirius, or Ich, is a parasitic infection that affects fish when they are stressed. The stress can be caused by poor water conditions, sudden temperature changes, illness, and overcrowding. When the fish get stressed, the immunity system becomes affected, allowing the parasitic infection.

This condition can be fatal if you don’t treat it immediately. In addition, it’s highly contagious; therefore, you must be careful.


  • Prominent white spots that look like sprinkled salt
  • White spots that are distributed across the body and gills
  • The fish become lethargic and weak and will not want to eat
  • The fish may spend more time gasping for air at the top of the tank
  • Your fish rubbing their side on the tank


When your fish has Ich, it’s advisable to see an aquatic specialist to help you with the treatment process. However, you can also start treatment by increasing the water temperature in your tank. This process helps speed up the parasite’s life cycle so the fish can heal much faster.

In addition, some aquarists use medicated tanks containing copper sulfate, potassium permanganate, and aquarium salt. Ich-X can also be used to treat this parasitic condition in freshwater fish. Watch for any secondary infections as you start treatment because they might kill the fish.

Anchor Worm

Despite the name, anchor worms are not a type of worm. They are a large parasitic crustacean called Lernaea crypinacea. They usually attach to your fish’s skin and feed on the blood and cells.

Although they affect all types of fish species, they are common in goldfish in a pond or aquarium. You can infect your fish if you bring in new species that already have the disease.


  • Red and inflamed scales
  • Visible worm-like parasites attached to the gills or body of the fish
  • Your fish will start rubbing its body against items in the tank
  • May become lethargic and slow


These parasites are not fatal to the fish but can lead to more severe infections. To treat the condition, you can pull them out of the fish using forceps.

Ensure you remove the entire worm to avoid leaving any part inside the fish. After removing the parasites, you can apply some antibiotics ointment on the scales.

You can also use antiparasitic products that contain potassium permanganate as a dip for tank treatment. Clean the entire tank to get rid of eggs, larvae, and parasites in the tank.

Freshwater Velvet (Gold Dust Disease)

Velvet, also known as Gold Dust, is caused by the Oodinium spp. parasites. They can be fatal and wipe out your entire tank. These parasites affect your fish only if they get stressed due to sudden water temperature, poor water quality, or sickness.


  • Your fish may scratch their bodies against the tank to remove the parasites
  • Rapid breathing
  • Yellow to gold dust-like specks on the body
  • Not eating and weight loss
  • Clamped fins
  • Peeling skin in severe cases


One of the best ways to treat this problem is by dimming the tank. This is because the Oodinium parasites use photosynthesis to get food. You can also increase the temperature in the tank by a few degrees to speed up the parasite’s lifecycle.

You can also use a copper-based medication for about 10 days to get your fish back to health. Products like SeaChem Cupramine could work well. In addition, you should also remove the sick fish from the community tank.

Gill Mites

Gill mites attach to your fish’s skin and feed on blood. As ectoparasites, they are found on the external surface of your fish.

You might not see them with the naked eye, but you can identify the symptoms. Gill mites enter your aquarium from new fish that have been introduced into the tank.


  • Gill covers remain slightly open
  • Your fish spend a lot of time on the surface, gasping for air
  • Reddening gills
  • The fish may be scratching against the tank


To treat gill mites, you’ll need a praziquantel-based medicine that’s effective against mites. You might also need to repeat the treatment process for about five days to kill the mites hatched in the tank completely. Treat your entire tank to avoid secondary infections.

Common Bacterial Infections

Fin and Tail Rot

Fin rot is one of the common fish diseases that is caused by Aeromonas spp. This condition is usually caused by unclean or poor water quality. In addition, it can also happen if you choose aggressive tankmates for your fish, known for fin-nipping.


  • Fraying or torn fins
  • A ragged tail
  • Decay at the fin edges
  • Your fish may have difficulty swimming


One of the ways to treat this condition is by having a 25%-50% water change. You can also remove the aggressive species from the fish tank. Additionally, there are antibacterial medications that can treat this problem, such as SeaChem KanaPlex.

Related: More about common Betta fish diseases

Mouth Rot

 This condition is caused by a fungus called Flavobacterium bacteria. Apart from the mouth, it also affects the gills and the body. Also known as Columnaris, it’s caused by poor water conditions, stress, and overcrowding that lowers your fish’s immunity system.


  • White, cotton-like patches on the mouth or gill
  • Body ulcers
  • Rotting mouth
  • Appetite loss


Since it’s caused by stress, you need to check the water parameters to improve the quality. You can also use medications in your tank, such as SeaChem KanaPlex.

Common Viral Diseases


This viral infection is caused by the iridovirus lymphocystis disease virus (LCDV). It can cause deformities because it affects the fins and skin. Lymphocystis will appear in your tank if you bring in new fish that’s already infected. Gouramis, killifish, and cichlids are the most affected.


  • White patches around the eye
  • Fish may have a problem breathing
  • Slow and lethargic fish
  • You may notice erratic swimming


Although there’s no treatment for this viral infection, the fish’s immune system will take care of it within a few weeks. To help with the treatment, ensure that the tank is not overcrowded and the water quality is okay.

Common Fungal Diseases

[Photo by Marius Masalar, Unsplash]

Body Fungus

Fish get fungal infections from Saprolegnia and Ichthyophonus hoferi. These infections are due to unclean water conditions. They also become prominent if you have decaying organic material in your tank. Body fungus affects your fish if it has open wounds.


  • Grey cotton-like growths on the gills, fins, and skin
  • The fish may become lethargic
  • Slight discoloration
  • You’ll notice erratic or slow swimming


You can treat this problem using medications like Ich-X or other antifungal medications. Maintaining good water quality makes you less likely to get a fungus outbreak. Additionally, ensure that your fish don’t have any open wounds.

Other Common Infections


If you notice that your fish are swelling, they could be having Dropsy due to kidney disease. Your fish will get kidney issues due to stress or kidney disease. This bacterial infection caused fluid build-up in the kidneys, leading to swelling.


  • A slightly swollen belly
  • Scales sticking out
  • Difficulty in breathing
  • Poor appetite


If your fish has Dropsy, it’s advisable to put it in a quarantine tank away from the stress. Unfortunately, this condition is quite fatal; therefore, your fish might die. Contact the aquarium store or local vet immediately if you notice that your fish has symptoms of Dropsy.

Swim Bladder

The swim bladder is an essential organ in your fish because it contains oxygen to keep your fish buoyant. Therefore, if it has a problem, the fish will have a problem swimming.

This problem is caused by poor water quality leading to stress. Additionally, it could also be due to fungal and bacterial infections. If you have new fish, they might have this problem if they were transported incorrectly.


  • Your fish is unable to stay upright
  • Issues swimming to the bottom or the surface
  • Swollen stomach
  • Erratic swimming
  • Lethargic fish


An aquatic vet might be the best option for this condition. They can release the air from the swim bladder to fix the problem. Additionally, you can also test the water quality and make changes to fix the problem.

How to Prevent Fish Diseases in Your Aquarium

Now that we’ve identified the common health conditions that affect your fish, you need to know how to prevent them. Fortunately, there are multiple things you can do at home to prevent these infections.

Here are some of them:

High-Quality Water

Always ensure that the water quality is well maintained. Monitor the temperature, pH, and other parameters based on the type of fish you have in your tank. When the water conditions are stable, your fish are less likely to get sick.

Provide a Quality Diet

When you keep any type of fish species, ensure that you feed them the right diet. Each species has its own needs, so you should pay attention to the type of food you provide. This will also boost the immunity system and keep your fish healthy.

Tank Observation

You can prevent some diseases by constantly monitoring your tank for any changes or signs of sickness. If detected early, some diseases can be controlled. You can remove the infected fish in time, especially if you are dealing with a contagious disease.

For issues like fin rot, you need to check whether you have aggressive tankmates that are fin-nipping. In addition, confirm that the new fish are not stressed, which lowers the immune system.

Quarantine New Fish

When you get new fish, you can place them in a separate tank first for a few weeks. This will give you time to monitor whether the fish is healthy, especially if you have a community tank. Once you confirm that the new fish is healthy, you can add it to the tank with the others.


[Photo by Biljana Martinić, Unsplash]

Fish are susceptible to several diseases. Fortunately, most of them can be treated at home or through medications. Identifying symptoms is critical in ensuring your fish get the treatment early enough.

You can prevent most of these diseases by maintaining the water parameters, feeding your fish quality food, and observing your fish. However, once you notice any issue, you can follow the treatment steps outlined above. In addition, you can contact an aquatic vet to advise you on the best course of action.


Jason Matthews

My name is Jason Matthews, and welcome to my website. When other kids were bragging about how their dog could sit and roll over, I was bragging about my latest Betta Fish and the cool sea castle I just added to his aquarium. 

Jason aquariume

🐠 Get Your Free Ebook: A Beginner's Guide to Aquariums - Sign Up Now!

Learn everything you need to know to keep fish, including setting up your tank, choosing the right fish, and maintaining water quality. As a subscriber, you'll also stay up-to-date on the latest aquarium products, special offers, and discounts.

Your privacy is important to us. You can trust that we will never share or sell your information, and we'll only send you relevant content.

Leave a Comment