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Red Eyes In Fish – Causes, Treatment And Prevention

red eyes in fish

Just because a fish has red eyes doesn’t mean there is a problem. Some fish breeds – such as the red-eyed tetra fish – are prized for their red round eyes, which are perfectly normal and healthy. However, however, red bloodshot eyes in fish of other species can indicate that your fish may be sick.

If you notice red eyes in one or more of your fishes, it is likely that an underlying infection is behind the scene. This condition can cause your fish to lose its eyes or sight, or even worse, death if it is not treated.

What are the possible causes of this red eyes in fish?


Red eyes in fish can result from a number of factors.

  1. Ammonia Poisoning

It can also occur in an established tank when too many fish are added at a time, when a filter fails due to an electrical or mechanical failure, or can be due to change in water conditions. In ideal water conditions, ammonia levels should be non-existent.

Causes to ammonia poisoning

Ammonia can enter the tank in several different ways. First through chemical treated tap water. Some water treatment companies use a chemical called chloramine bound to ammonia as a more stable disinfectant for city water systems. Using tap water treated with this chemical is a recipe for aquarium disaster.

Overfeeding and lack of cleanliness lead to the build-up of bacteria that eat this extra substance, resulting in an ammonia byproduct. Fish also contributes to ammonia poisoning too leading to rising ammonia levels in tank.

When a fish eats the food, the protein-building process (in order for them to grow) can produce byproducts that enter their blood. This results in leakage of ammonia into their gills and tank.

Symptoms of Ammonia Poisoning in Fish

Ammonia poisoning can happen suddenly or over a period of a few days. Initially, the fish may seem to come often to the surface gasping for air. Their eyes and gills will start to turn red, making it look like they are bleeding. In some cases, you may find fish laying on the bottom of the tank with their fins buried.

As damage from ammonia poisoning continues, the fish’s tissues begin to deteriorate, which is manifested by bloody patches on their eyes and fins. You will notice that the fish starts bleeding both internally and externally. Then, they eventually die.


If the ammonia level in your tank rises above 1 ppm (parts per million) on a standard test kit, begin treatment immediately. Lowering the pH of the water will provide immediate relief, as well as replace 50 percent of the water. Several water changes may be required within a short period of time to drop the ammonia below 1 ppm.

At this point, restrict feedings so that excess waste is minimized. In case of very high ammonia levels, feeding needs to be discontinued for several days. And of course, no new fish should be added to the tank until both ammonia and nitrite levels have dropped to zero.

  1. Excessive Nitrate

Excess nitrate

When fish are exposed to slowly rising nitrate levels over a period of time when regular tank maintenance is not performed and cause harm to your fish.

Symptoms include;
  • loss of appetite
  • rapid gill movement, higher respiratory rate
  • listlessness, acting astonished
  • loss of balance, disorientation
  • curl from head to tail (advanced step)
Treatment includes;
  • Make several small water changes
  • To reduce nitrate levels, slow, controlled water changes will be necessary.
  • Ask about recommended nitrate values ​​for any new species. Before buying a new species of fish, test your water and pay attention to the pH and nitrate levels. At the aquarium store, ask the clerk to test the water to verify that the pH and nitrate levels are close enough to those found in your home’s tanks.
  • Use filter media that removes nitrates. Whenever nitrates are a frequent problem, nitrate removal filter media is a helpful tool.
  • Feed less. Be sure to feed your fish enough food to keep the fish healthy. Nitrate levels should be maintained naturally once feeding practices are corrected.
  1. Septicemia

What is septicemia and how do fish get infected? Septicemia is an infection located in the bloodstream through consuming foods infected with bacteria.


There may be redness at the base of the fish’s fin, streaks of blood all over the fin and body, small hemorrhages around the eyes. Lethargic dull, behavior and loss of appetite may also be present.


Systemic bacterial infections caused by a variety of bacteria, including Aeromonas, Pseudomonas and Vibrio. Illness often results from poor water quality or parasitic infestations or other infections.

These bacteria enter the bloodstream and spread to tissues causing inflammation and damage. Inflamed blood vessels in the skin and at the base of the fin stand out.

Blood vessel and heart tissue damage causes bleeding and results in leaking of body fluids into the abdomen, which can lead to dropsy.


Test your water treatment with kanacin or tetracycline as well as a medicated food if the fish will eat it. If parasites are suspected, all fish in the tank should be treated with antiparasitic medication. It may be helpful to use salt to help restore osmotic balance.

  1. Bacterial Infection

They often follow parasitic infection, abrasion or physical injury, but can also be caused by prolonged exposure to poor water quality and/or poor diet. Another common reason is the removal of the fish’s protective mucous membranes or scales during netting.

Bacterial infections manifest in many ways, but common symptoms include a white film on the body or fins of the fish, red eyes, cracked fins, and hermorhaging or open sores (cysts) on the body and mouth.

  • Effective treatments include levamisole, metronidazole or praziquantel. Metronidazole and praziquantel are especially effective when used as a food soak, these treatments should be used with caution so as not obstruct the tank’s biological filter.
  • Read all package directions before using any medicine and avoid mixing different drugs in the aquarium.
          5. Overstocked Aquarium

Another possible reason for red eyes in fish can also be that there may be overstocked in the tank and there may not be enough media to break down the ammonia. If you are new to the fish keeping, you might find it difficult to know if your tank is over-stocked or crowded.

Once you know a few important things, you’ll understand if you have too many fish in your tank and therefore overstocked.

  • Stress
  • Disease
  • Bullying
  • Poor water quality – nitrates, ammonia, cloudy water
  • stunted growth
  • Fish gasping
  • Algae blooms
  • Strange Behavior Patterns
  • Excess fish waste not being filtered

When you add more fish to your tank and it becomes overstocked, not only will it be more difficult to maintain, but the fish will begin to suffer and their quality of life will decline. Due to this the death of other fish is also possible.

How to prevent red eyes in fish

  • Keep the tank clean. Keeping your tank clean can really help in reducing nitrates. Immediately remove all uneaten food. Clean water is usually the best medicine for any fish disease. One thing to consider is the quality of the food you feed your fish, good quality food helps maintain water quality too!
  • Perform regular filter maintenance. Regular cleaning and changing the carbon filter media will go a long way in keeping nitrates away.
  • Don’t overstock your aquarium.
  • Use filter media that removes nitrates. Whenever nitrates are a frequent problem, nitrate removal filter media is a helpful tool.

Also, when you notice a red-eyed fish it is best that you quarantine it to avoid spreading it to other fish. Once these diseased fish are still in the tank, it can affect your entire aquarium and kill all your fish! So without any doubt, it is absolutely necessary to keep the new fish separately.

How to quarantine red eye fish

1.Equip your tank.

Buy a quarantine tank that is at least 10-20 gallons. Purchase additional supplies, including a filter, a heater, a power head to stir the surface, and a fish net to keep the water clear so you don’t infect the fish in your main aquarium.

  • Get an aquarium test kit for pH, ammonia, nitrates and nitrates if you don’t already have one to make sure the tank water quality is high.
  • The bigger the fish, the more space you’ll need to keep the quarantined fish.
2 Fill the tank with water.

Before adding water, thoroughly clean the quarantine tank with warm water. Keep it in a dark place to keep your fish cool. Then use the water from your main tank to fill the quarantine tank. This can ensure that your fish get used to their new aquarium quickly.

  • Avoid using soap when cleaning the tank as the chemicals can be toxic to fish.
  • Add new water to the main tank by adding distilled water you treated so that it has similar properties.

3 Think of your quarantine tank as an extension of your main tank. Place the filter, heater and power head in the tank. Having some decorations and hiding places can also help your fish feel more comfortable in their new surroundings.

4 Check the quarantine tank environment. Allow the filter to cycle a few times and turn on the power head to clean and aerate the water in the quarantine tank.

Take the water temperature to make sure it is the same as the main tank. Use your test kit to make sure the pH is even or the same as in the main tank. Ensuring that the quarantine tank environment is the same or close to that of your main tank can maintain the vitality and health of your fish and their offspring.

5 Remove fish from main tank.

Fill a plastic bag with tank water so that you can place the fish you want to transfer into it. Using your new tank net, scoop up the fish you wish to quarantine. Then put the fish in a plastic bag and move it to the new tank. Removing your fish in this way can reduce its stress and help maintain its vitality.

  • If you have new fish, keep them in their plastic bags to avoid shock.
6 Acclimate your fish in the quarantine tank.

Leave the bag in the water for 15 minutes to allow the fish to slowly adjust to the water temperature. Cut the bag open the bag and let the fish swim free in the quarantine tank. Taking the time to acclimate your fish to a quarantine tank can reduce the risk of shock to the fish, which can harm its health.

Treatment and return of quarantined fish

1 For 3-4 weeks, watch the health and vitality of your quarantined fish closely. Look for signs of potential problems to ensure immediate tank removal and treatment from the quarantine breeding tank.

  • White spots or velvety spots on the body
  • Missing scales or incomplete fins
  • Cloudy or bulging eyes
  • Ulcers or other lesions
  • Rapid breathing, gasping on the surface and trembling
  • Erratic swimming
  • listlessness
  • Bubble nest from male fish
2 Treat any illness.

If one of your quarantined fish is sick or becomes ill, determine the best course of treatment. This can include things like cleaning or improving water quality by giving fish medication.

To ensure that the fish can recover without any additional problems, extend the quarantine by at least two weeks from the time the treatment begins. Once the fish appears healthy, release it into quarantine for another week.

3 Take the fish back to the main tank.

Once your fish is healthy, remove it from the quarantine tank with a new net. Place the fish in a plastic bag with the water in the main tank. Then put the sealed plastic bag in the main tank for 10-15 minutes before your fish starts swimming free.

  • Avoid adding quarantine water to your main tank, as it may still contain drugs harmful to your other fish.
4 Disinfect your tank and equipment after the quarantine is over.

Mix 200 mg of bleach in one liter of water in the tank. Use more for larger tanks. Clean the tank surfaces and equipment with the bleach mixture and rinse thoroughly with clean water when finished. Allow the tank and equipment to air dry, which can kill any germs. Then put the tank in a clean, dry place in your home.


There you have it, how to get rid of red eyes on fish.

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