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The most common fish diseases and how to protect your animals

Common fish diseases
Mistakes in keeping and feeding can lead to fish diseases, among other things. Photo: Getty Images/LordHenriVoton

November 26, 2024, 12:40 pm | Read time: 4 minutes

Diseases can spread quickly in an enclosed space such as an aquarium. PETBOOK provides an overview of the most common fish diseases and how to recognize them.

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Like any other living creature, fish can also become ill. The causes are varied, from parasites to bacterial or viral infections. Understanding the most common fish diseases is crucial to recognizing symptoms early, taking appropriate countermeasures, and preventing their spread among the population. In this overview, we take a look at the most common fish diseases and how to recognize them.

Infectious dropsy

Infectious dropsy is a highly contagious fish disease that is becoming increasingly common, especially in ornamental fish. Caused by a bacterial infection, this disease causes fluid to accumulate in the abdominal cavity of the fish. This leads to swelling of the abdomen and also the eyes. The afflicted fish become increasingly restricted in their movement and progressively weaker. Other symptoms include inflamed, pale skin, pale gills, and protruding and detached scales. If the disease is recognized at an early stage, it can often be treated successfully.1

Fin rot

Fin rot mainly affects ornamental fish such as guppies and goldfish. A bacterial infection causes the fins of the fish to lose their color and fray. The disease is highly contagious and leads to the death of the animals if left untreated.2

Fish mold

Fish mold is caused by an infection with fungi of the genus Achyla or Saprolegnia and is a common fish disease that particularly affects animals with a weakened immune system.

At the beginning of the disease, white spots form on the eyes, fins, mouth edges, and nostrils of the fish. Over time, cotton wool-like deposits then form in these areas. The disease has more serious consequences for the fins. These can stick together, fray, and ultimately disintegrate.3

Fish tuberculosis

Fish tuberculosis also mainly affects fish that already have a weakened immune system. The disease is triggered by an infection with mycobacteria, which occur naturally in the aquarium. Infected fish do not always show symptoms. The disease can progress either gradually or rapidly. Infected fish can be recognized by protruding eyes, pale colors, and changes in scales.4

Velvet disease

Velvet disease owes its name to the appearance of the infected fish. They look as if they are covered in velvety dust. This fish disease is caused by dinoflagellates, which are single-celled organisms approximately 0.1 millimeters in size and can be present in any saltwater aquarium.

The velvet disease causes the affected fish to breathe less easily and produce more mucus. It is also noticeable that they are generally more sluggish and rub themselves more often.5

Poisoning due to ammonia or nitrate

Too much food or poor quality food in the aquarium can cause toxic substances such as ammonia or nitrate to accumulate. This can result in fish poisoning. Symptoms such as shortness of breath cause the pale fish to panic and try to gasp for air at the surface of the water.

White spot disease

This infectious disease is caused by the single-celled parasite Ichthyophthirius multifiliis. This bores into the mucous membrane of the fish, causing white raised spots. If detected early, the disease can be cured. At an advanced stage, it can lead to the death of the fish as the skin increasingly detaches from their bodies.6

More on the topic

These factors favor diseases in the aquarium

The most common fish diseases result from a combination of different factors. These lead to a weakening of the fish’s immune system – which makes them more susceptible to diseases. One common factor is poor water quality and incorrect water values. Unsuitable water values, such as excessive water hardness or water contaminated by food or impurities can affect the health of the fish. Unsuitable planting of the aquarium can also have far-reaching consequences. Before buying any plants, you should, therefore, find out whether they are suitable for your fish species.

Nutrition also plays a major role in the health of fish. Particular attention should therefore be paid to the quality of the fish food – but the quantity of food should not be ignored either. Stress can also contribute to a weakening of the fish’s immune system. This can be triggered by incorrect socialization of the animals, for example. Some fish species do not get along with each other due to different lifestyles or hunter-prey relationships.

This article is a machine translation of the original German version of PETBOOK and has been reviewed for accuracy and quality by a native speaker. For feedback, please contact us at info@petbook.de.

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Sources

  1. fischlexikon.eu, "Infectious dropsy" (accessed on 26.11.2024) ↩︎
  2. triopsgalaxy.de, "Fin rot in fish - causes and preventive measures" (accessed on 26.11.2024) ↩︎
  3. aquaristik-profi.com, "Fungal infection: diagnosis, causes & treatment" (accessed on 26.11.2024) ↩︎
  4. aquaristik-profi.com, "Fish tuberculosis:Diagnosis, causes & treatment" (accessed on 26.11.2024) ↩︎
  5. interaquaristik.de, "Velvet disease (Piscinoodinium)" (accessed on 26.11.2024) ↩︎
  6. koelle-zoo.de, "White spot disease in fish" (accessed on 26.11.2024) ↩︎
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