How to Treat Anemia in Fish

Catfish gills

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Anemia in fish works a little differently than it does in humans. Fish anemia not commonly caused by an iron deficiency but a protein deficiency from a poor diet. Most of the time, anemia occurs when feeding your fish old flakes or pellets. As long as your fish is still hungry, this is a relatively easy fix without any long-term consequences. If your fish refuses to eat, you will require veterinary assistance to get your fish back in shape.

What is anemia in fish?

Anemia in fish, as in other species, is a lack of red blood cells. There are many potential causes, including dietary insufficiency, blood-sucking parasites, such as leeches, aggressive tankmates, cancers, and a secondary symptom of many diseases processes, including a few viruses. No matter the cause, lack of red blood cells has a direct impact on your fish's appearance and behavior.

Symptoms of Anemia in Fish

  • Pale gills
  • Lethargy
  • Increased respiration
  • Negative buoyancy

Fish gills should be red when they are healthy. Pale pink or white gills are a cause of serious concern in fish. Gills can be pale for many pathologies and are not pathognomonic for anemia.

Depending on your species, your fish may not be swimming all the time. Bottom-dwelling fish, such as catfish, and those with long fins, such as bettas, do not swim as much as other fish and long rest periods are normal.

Respiration and effort are highly subjective. If you suspect your fish may be having difficulty breathing, compare their gilling to others in the tank. You can also take a short video and use it to compare various periods.

Buoyancy disorders can occur for many reasons. Depending on your fish's species, it may require surface air to inflate its swim bladder. An anemic fish may have a secondary buoyancy disorder from stress or secondary to decreased energy.

Causes of Anemia

The most common cause of anemia in pet fish is a poor diet. Many fish owners don't carefully monitor their fish's diet and might feed long-expired food. Protein is required in all animal diets to produce hemoglobin, the iron-containing molecule in red blood cells. Without enough protein in the diet, the animal doesn't have enough hemoglobin to transport oxygen around its body. Other protein deficiency signs include increased mortality, fin rot or erosion, scoliosis, decreased body condition, lethargy, and an increase in secondary diseases.

All dry fish foods should be fed for 6 months, then replaced. After this period, there is considerable loss of water-soluble vitamins, including vitamin C. Flake foods will spoil faster than round, pelleted diets, and should be replaced more frequency. Unless the food comes pre-frozen, it's not a good idea to freeze most fish food; it could decrease the nutritional value.

Protein requirements for fish vary widely and not many scientific studies are available for most ornamental pet fish species. Considerable data is available for aqua-cultured species which can be extrapolated to many similar pet species. Consult with an aquatic veterinary specialist to determine the best diet for your fish.

Many hobbyists are quick to jump to hemorrhagic septicemia, a known viral pathogen in goldfish and idiopathic in some other species. Also known as Cyprinid Herpesvirus-2 and goldfish hematopoietic necrosis virus, this disease is an OIE reportable disease and extremely rare in pet fish. Other viral disease can also contribute to anemia in some fish species and will require diagnostic testing using gill, kidney, spleen, or liver tissues to confirm.

Passive fish in mixed species tanks with aggressive eaters are also at risk for anemia because of lack of food in general. During feeding time, be sure to spread out the foods throughout the tank, rather than concentrated in one area. This will allow all inhabitants to get their fair share.

Aquatic leeches can also cause anemia in fish, although they are not common in captive-bred species. Wild-caught species carrying leeches can see considerable blood loss anemia. Most commonly, the leeches are inside the mouth and operculum, making them hard to diagnose.


Once anemia has been diagnosed in your fish, you should focus on correcting any secondary pathologies, such as secondary infections or buoyancy disorders and dietary supplementation. Depending on the severity of your fish's anemia, it may take days to weeks to months for full resolution. During this time period, managing stress is critical to supporting your fish's recovery. This includes maintaining good water chemistry and minimizing aggression from other fish.

Iron supplementation won't be needed unless your fish is sufficiently large to take oral supplements under direction of a veterinarian. This is only recommended in very serious anemia cases with heavy blood loss. Heavy iron levels in the water are considered to be very harmful and can lead to increased incidence of many cancers.

How to Prevent Anemia

As with most fish pathologies, the best way to prevent anemia in your fish is to provide a healthy environment and fresh diet. Even though we cannot be certain that any given diet is 100% correct for a particular species, providing adequate protein, fat, and vitamin content is critical to the survival of all fish. Discuss any dietary or health concerns with your aquatic veterinarian to ensure the overall health and well-being of your fish.

Article Sources
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