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Fish Diseases

Fish Diseases

Fish Diseases

Fish Diseases typically fish have quite robust immune systems, designed to fend off a number of ailments and parasites. However, fish that are stressed out or living under less-than-ideal environments become significantly more susceptible to illnesses. If you feel that something with your fishes does not seem right, or if you think that they are showing signs of illnesses, this article might help you figure out what is going wrong.

Most Common Fish Diseases and Their Symptoms:

Anchor Worms Fish Diseases:

Despite its name, Anchor Worms are not exactly worms but a huge parasitic crustacean. This crustacean belongs to the Learnea species, and can reside on your fish. Anchor worms attach to the fishes’ skins and bury their heads deep into the fishes’ muscles.

The main signs of Anchor Worms are red, inflamed scales. Upon closer examination, you may even be able to notice the body of the Anchor Worms parasites jutting out of your fish’s skin. Their parasitic bodies seem like green-and-white threads attached to the fish. You might also notice your fish rubbing its bodies against various items in the tank as a way to relieve the itch and discomfort that comes with Anchor Worms.

Ammonia Poisoning:

Your fish tank can accumulate dangerously high levels of ammonia. Ammonia poisoning is particularly common in newly setup tanks or tanks where a large number of fishes are added simultaneously.

Symptoms of ammonia poisoning include purple or red gills, and fish coming up to the water surface and gasping for breath.

Bacterial Infections Fish Diseases:

Although fishes can get a bacterial infection at any time, these infections are particularly likely to happen when your fish has an injured body part. Other causes of bacterial infections include poor diet or water quality, both of which can weaken your fish’s immune system and make it easier for the bacteria to attack. Aeromonas Salmonicida is the most common type of bacterial infection found in fishes.

The most common signs of a bacterial infection are:

  • Ulcers (normally on the gills)
  • Red spots throughout the body
  • Swollen abdomen
  • Enlarged eyes

Nitrite Poisoning:

If ammonia poisoning is not addressed in a timely manner, it can evolve into nitrite poisoning. Remember that nitrite is more harmful than ammonia, which is why you should frequently test your water tank to ensure that nitrite levels are down to zero.

If your fish is suffering from nitrite poisoning, you can expect their gills to turn brown or tan. Secondly, as is the case with ammonia, the presence of excessive nitrite will cause your fish to gasp at the water surface.

Constipation Fish Diseases:

Infrequent bowel movements can lead to constipation, and can cause fishes to become quite ill. The two main causes of constipated fishes are improper diet and parasitic infections, both of which can render a fish unable to normally pass feces.

Fishes who are constipated will often develop an enlarged abdomen. Other than that, chronic constipation can also lead to swim-bladder disease, of which buoyancy problems are a common sign.


Flukes are parasites which commonly target the gills. The two most common types of Flukes found in fishes are Gyrodactylus and Dactylogyrus. Flukes commonly enter an aquarium when you add a fish that has already been infected with the parasite.

Fluke parasites attack and damage a fish’s gills and skin, often causing secondary bacterial infections.


Dropsy is a term used to describe the swelling occurring in fishes that are suffering from kidney disease. The most common causes of kidney disease in fishes are Polycystic Kidney Disease and long-term stress.

As you might have guessed, swelling is the primary symptom of Dropsy. The swelling generally occurs in the abdominal region, can range from mild to severe, and sometimes even causes a fish’s scales to stick out and give it a pinecone-like appearance.


Pop-Eye is generally caused by a bacterial infection, but may also be a sign of a Vitamin A deficiency, poor water quality, or mass behind the eyes.

As the name suggests, Pop-Eye will cause your fish’s eyes to bulge out of their sockets (which is also why this condition is quite easy to diagnose).

Freshwater Velvet:

Freshwater Velvet (also known as ‘Gold Dust Disease) is quite lethal, and does not take long to wipe out every sign of life in a water tank. The Oodinium Limnetic and Oodinium Pillularis parasites are the most common causes of Velvet. While Velvet is present in a lot of aquariums, it only creates issues in fishes that are sick, stressed, being transported, suffering from an abrupt change in temperature, or residing in poor quality water.

Fishes suffering from velvet will scratch their bodies against various items in the aquarium as an attempt to get rid of the parasites attached to their skins. You can also expect to see a few or all of the following signs:

  • No or reduced appetite
  • Loss of weight
  • Rapid breathing
  • Lethargy
  • Holding fins next to the body
  • A rust or yellow color spreading throughout the body
  • Skin peeling

Hemorrhagic Septicemia:

Hemorrhagic Septicemia is caused by the Piscine Novirhabdovirus, and is almost always deadly.

Fish suffering from this disease will develop bleeding on their skin, muscles, and in their internal organs, seen as tiny red dots spread throughout the skin. Other symptoms include:

  • Dark-colored body
  • Pale gills
  • Bulging eyes
  • Accumulation of fluid in the body

Mouth Rot:

The Flavobacterium bacteria are the main culprit behind mouth rot in fishes. These bacteria usually develop in poor water conditions, and attack fish that are already sick or stressed out.

If your fish is suffering from mouth rot, you might be able to notice a cotton-like appearance surrounding its mouth. If left untreated, the condition will cause the skin around your fish’s mouth to start rotting.

Final Word on Fish Diseases:

To sum up, fishes can suffer from a wide range of ailments. However, most of these ailments, especially when caught early, are very treatable. However, like always, prevention is better than cure, and by maintaining ideal water quality, a good diet, and a clean tank, you can keep many of these issues from developing in the first place.