Caring for Fish in Aquaponics

Fish health and care are critical and essential to an aquaponics system's overall health and function. So understanding your fish needs is an integral part of running a successful aquaponics system because waste production slows if the fish are unhealthy, resulting in poor plant growth and harvest.

Keeping your fish healthy and free from diseases will go a long way toward ensuring that your system is running smoothly. This article discusses the critical aspects of fish health in aquaponics, including managing and preventing fish diseases.

Koi Fish in Aquaponics

Caring for Your Aquaponics Fish

Like plants, it is best to wait until the system is cycled and the biofilter is fully functioning before adding fish to your aquaponics system. There are several essential factors that you should consider in caring for fish in your aquaponics. These factors are:

1. Fish Selection

Choose the best fish species that are suitable for your system, climate, and location. The most common fish in aquaponics are tilapia, carp, barramundi, jade perch, catfish, trout, cod, salmon, and bass. It is also essential to know your local fisheries regulation because not all fish are legal to be purchased and grown in some locations.

2. Acclimating The Fish

Acclimatize new fish to the water in your fish tank to avoid fish stress. To acclimatize the fish, slowly allow the temperature to balance by floating the sealed transportation bags with the fish inside the fish tank. Do this for 15 minutes and add a small amount of water from the tank to the transport water with the fish to slowly acclimate the fish. This should take at least 15 minutes, and you can add the fish to the fish tank.

3. Fish Feeding

The fish-feed ratio provides a way to balance the components of an aquaponics system. Fish feed rates vary according to the growth stage of the fish.

  • During the grow-out stages, the recommended fish feeding rate is 1 to 2 percent of their body weight per day. So, if the fish stocking density is 10 to 20 kg per 264 gallons, you must provide 200 g of fish feed daily.
  • During the first two to three months, small fish (like 50 g tilapia fingerling) eat about 3 percent of their body weight daily. So if you have an initial stocking of 40 fingerlings and weigh 2000 g together, they will consume approximately 60 g of fish feed per day.
  • After two to three months, the feeding rate will be 80 to 100 g of fish feed per day. (It is because the 40 fingerlings will have grown to 80 to 100 g each, and the total weight will be 3200 to 4000 g)

    Fish Health and Behavior

    The primary indicator of fish health in your aquaponics system is their behavior. It is essential to recognize the behavior of your fish and look for signs of fish stress, disease, and parasites to maintain healthy fish.

    Here are some tips on maintaining healthy fish in your aquaponics system:

    1. Observe fish before and after daily feeding and note how much feed is eaten.
    2. Observe and take notes of the fish's behavior and appearance daily.
    3. Understand the signs of fish stress, disease, and parasites.
    4. Maintain a low-stress environment with consistentgood water quality, specific for the fish in the system.
    5. Use the proper stocking density and feeding rates.

    Healthy Fish Behavior

    Healthy fish in your system shows the following behavior:

    1. Extended fins and straight tails.
    2. A graceful pattern of swimming. No lethargy. However, catfish often sleep at the bottom of the fish tank until they wake up and begin feeding.
    3. A healthy appetite and not shying away at the presence of the feeder.
    4. No marks, discolored blotches, streaks, or lines.
    5. Not rubbing or scraping on the sides of the fish tank.
    6. Sharp, clear, and shiny eyes.

    Overstocked Koi Fish in Aquaponics

    Fish Diseases in Aquaponics

    Several conditions can cause fish health problems in your aquaponics system: fish disease, parasites, fungi, and bacteria. These can all appear in your fish tank and quickly spread disastrous effects on the fish. The chance of fish disease or stress is especially high when you introduce new fish or add new water to your system, as the new fish might have brought diseases with them.

    Prevention is the best way to prevent disease in fish, and recognizing the signs of fish diseases can help you avoid the loss of fish in your aquaponics system. In preventing fish disease, it is essential to check your fish regularly for any of the following signs:

    • Check their appearance regularly because several parasitic and fungal infections can be visible on the fish skin, scales, or fins.
    • Check for behavior changes, such as your fish becoming lethargic, refusing to eat or changing feeding habits, changing swimming patterns, odd position in the water, head, or tail down, difficulty maintaining buoyancy, and fish gasping at the surface.
    • If your fish looks bloated or its scales seem raised, it also indicates health concerns.

      Most external signs of disease are:

      1. Ulcers on the body surface, discolored patches, and white or black spots.
      2. Fin rot, ragged fins, or exposed fin rays.
      3. Abnormal body configuration, twisted spine, and deformed claws.
      4. Swollen appearance and cotton-like lesions on the body.
      5. Exophthalmia or swollen popped eyes.

        What are The Causes of Fish Disease?

        Fish diseases can be introduced by adding new fish, poor water quality, live food, invertebrates, or equipment used in the system. Fish also carry bacteria, viruses, fungi, and parasites like other animals.Though not all these bacteria are harmful, some of these microorganisms, called pathogens, can potentially cause fish diseases. 

        The following factors can cause fish disease in your aquaponics system.

        • Adding new fish to the system
        • Environment or poor water quality
        • Fish stress
        • A poor or unbalanced diet
        • The equipment used in the system is not suitable for the fish.
        • Not getting along with other fish species in the fish tank.

          Common Fish Diseases

          1. Fish Fungus 

          Also known as cotton wool disease or fuzzy fish, the fish fungus looks like a cotton-like growth on the skin or fins. Fungal spores are common in poorly maintained tanks, poor water conditions, or damaged fish tissues from wounds. 

          Symptoms of Fish Fungus

          • Abnormal behavior
          • Open sores
          • Cotton-like growths on the body (white, brown, or gray color)
          • Bruised-looking and reddish eyes. 


            The first important thing you need to do is awater test to establish if poor water conditions cause fish disease. If there are other problems, such as ammonia and nitrite levels, then you must ensure that ammonia and nitrite levels are within their ideal range. 

            Carp Fish in Aquaponics

            2. Fish Stress

            Stress can be detrimental to fish, just as it is for humans. Prolonged fish stress can result in bad health outcomes.

            Stress in fish can be caused by:

            • Fast temperature changes or temperature is outside of the ideal range.
            • Poor water quality, pH, high nitrate, nitrite, and ammonia levels.
            • Bullying by other fish in the fish tank
            • Low dissolved oxygen, pump failure, or power outages

            Symptoms of fish stress:

            • Fish are skittish and easily disturbed.
            • Gasping at the surface
            • Poor Appetite
            • Strange swimming patterns
            • Rubbing or scraping at the sides of the tank
            • Physical Injuries
            • Improper fish handling
            • Improper feeding 
            • overcrowding in the fish tank

            Avoid and treat fish stress by:

            • Cleaning and maintaining the water quality in your system.
            • If your system has visible solids in the water, fit a filter or settlement tank.
            • Feed fish with correct feeding rates and remove uneaten fish food after feeding.
            • Ensure that your system is within the parameters of pH, ammonia, nitrites, and nitrates.
            • Ensure enough aeration.
            • If there is an identifiable fish bully in the tank, remove the bully fish.
            • Minimize scooping fish out of the tank for inspection (only do this if necessary) and reduce the frequency of opening and closing the tanks.
            • Treat the disease immediately once identified.

              3. Nitrite Poisoning

              A new aquaponics system is more vulnerable to nitrite poisoning, especially when beneficial bacteria do not yet colonize them. However, nitrite poisoning is not just limited to new systems; established aquaponics systems can have nitrite poisoning when the nitrites level goes over six ppm.

              Nitrites poisoning can be caused by:

              • Overfeeding the fish
              • Overstocking
              • Improper filter maintenance
              • Washing the grow bed because it also washes away bacteria

              Symptoms of nitrite poisoning:

              • Difficulty breathing
              • Darker gills
              • Tan or brown gills.
              • Faster gill movement
              • Swimming near the surface
              • Lethargy
              • Redness around the eyes and fins

              Treatment of nitrite poisoning:

              Lower the nitrite level in the fish tank by:

              • Change 25 - 50% of the water in the fish tank with good quality water, and keep changing the water until the ammonia and nitrite level is zero.
              • Stop or reduce feeding, and do not add new fish to the fish tank until the ammonia and nitrite levels are normal.
              • Remove uneaten fish food and clean the fish tank.
              • Ensure that the tank has enough aeration or add an extra aerator.
              • Adding half an ounce of salt for each gallon of water can prevent methemoglobin buildup. It will also minimize nitrite's influence to strip oxygen from the bloodstream. It is suggested that 1lb of salt is an effective dosage for 150 gallons of water. But salt does not evaporate, so take note of when and how much salt you add to your tank.

                  Unhealthy Dead Fish

                  How to Prevent Fish Diseases

                  1. Purchase healthy fish from a reliable and reputable fish supplier.
                  2. Quarantine new fish in a separate tank before introducing them into an established fish tank.
                  3. Feed the fish with a proper, varied, and well-balanced diet.
                  4. Keep your system's water quality clean at all times and ensure that it is within the critical water quality parameters of pH, ammonia, nitrites, nitrates, and the temperature of your fish.
                  5. Ensure enough aeration to keep the DO as high as possible.
                  6. Remove uneaten fish food from the tank.
                  7. Ensure that the water is from a good source, clean, and free of chlorine.
                  8. Make sure that the fish tank is in an excellent shaded place.
                  9. Follow the standard hygiene procedure by washing hands and using clean gear or equipment.
                  10. Treat the disease as soon as it is identified.


                  Fish health in your aquaponics system may also be affected by improper salinity, too much aeration, and lack of food. However, with proper aeration and the right fish food, these factors will not affect the health of your fish.

                  In managing fish health in your aquaponics system, keeping your water within its parameters, giving your fish the right fish food, andfollowing the aquaponics maintenance tips are essential. Thank you for reading, and subscribe to ournewsletter for more aquaponics updates.

                  1 Response



                  January 26, 2024

                  hello good day good people!

                  l have been deeply following your information regarding sustainable Aquaponic system, indeed i have learned so much up to this level all l hope to execute is practicals and maintenance of the whole system.but so far thank you so much for the whole information because is going to uplift my knowledge on my journey of looking forward to start my aquaponic system to response on the new technological system that is aimed at higher organic food production while minimizing carbon emissions that destruct the biosphere , water and environment.

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