The Importance of Fish Health in Aquaponics

The Importance of Fish Health in Aquaponics

Fish plays a vital role in aquaponics. They produce the waste that the plants need to grow and thrive. So understanding what fish needs is essential in running a successful aquaponics system because if the fish is not healthy, their waste production will slow, which will result in poor plant growth and harvest. If you want a successful aquaponics system, preventing fish diseases should be your primary concern. This blog discusses the importance of keeping your fish healthy and happy to have a successful aquaponics system.

Aquaponics Fish Selection

One of the most important decisions you’ll have to make when starting an aquaponics system in which fish species to use. To be successful, you need to carefully select fish that will thrive in your climates and location because different fish thrive at different temperatures and pH levels.  

Aquaponics allows growers to raise a wide variety of fish species, but the most common aquaponics fish species are tilapia, carp, barramundi, jade perch catfish, trout, murray cod, largemouth bass, koi, and goldfish. 

Acclimating Aquaponics Fish

In adding fish to the system, it is essential to acclimatize the fish first, to remove the stressful factors that can cause death to the new fish. The two simple ways of acclimating your fish are:

  1. Keep the new fish in a small aerated container with their original water and slowly add water from the fish tank over a day. 

  2. Slowly allow the temperature to equilibrate by floating the sealed transportation bags containing the fish in the fish tank for at least 15 minutes. Then slowly add a small amount of fish tank water to the transportation bag.

Fish Feeding

Fish food choice and fish food nutrient availability can affect the maintenance cost of your system. Fish requires the correct balance of proteins, fats, carbohydrates, vitamins, fats, and minerals to thrive. 

Commercial feed pellets are highly recommended for small-scale aquaponics systems, especially at the beginning. You can also feed homemade fish food to your fish, but special attention must be given because sometimes they are not balanced in the essential nutritional components needed by the fish.

Fish Feeding in Aquaponics

Fish Diseases in Aquaponics

Several conditions can cause fish health problems in your aquaponics system: fish disease, parasites, fungus, 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:

1. Check their appearance regularly because several parasitic and fungal infections can be visible to the fish skin, scales, or fins. Most external signs of disease are:

  • There are ulcers on the body surface, discolored patches, and white or black spots.
  • Fin rot, ragged fins, or exposed fin rays.
  • Abnormal body configuration, twisted spine, and deformed claws.
  • Swollen appearance and cotton-like lesions on the body.
  • Exophthalmia or swollen popped eyes.

2. Check for behavior changes, such as your fish becoming lethargic, refusing to eat or changing feeding habits, changing swimming patterns, odd position in water, head or tail down, difficulty in maintaining buoyancy, and fish gasping at the surface.

3. If your fish looks bloated or their scales seem to be raised, it also indicates health concerns.

Healthy Fish Behavior

Healthy fish 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.


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. Like other animals, fish also carry bacteria, viruses, fungus, and parasites. Though not all of these bacteria are harmful, some of these microorganisms, called pathogens, can 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.
  • Equipment used in the system is not suitable for the fish.
  • Not getting along with other fish species in the fish tank.

Common Aquaponics 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 tissues of the fish 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 a water test to establish if poor water conditions cause fish disease. If there are other problems, such as ammonia and nitrite levels, you need to ensure that ammonia and nitrite levels are within their ideal range.


Fish Diseases in Aquaponics
2. Bacterial and Parasite Infections

Fish affected with ectoparasites, molds, and bacterial gill contamination can benefit from salt bath treatment. Salt baths are toxic to the pathogen but not fatal to the fish.

How to Use Salt Bath Treatment:

  1. Remove the infected fish from the fish tank and place it into a salt bath. 
  2. The salt bath concentration should be 1 kg of salt per 100 liters of water. 
  3. Place the affected fish in the saline solution for 20-30 minutes and then transfer to an isolation tank containing 1-2 g of salt per liter of water for 5-7 days. 
  4. Do not use the salt bath water when moving the fish back to the fish tank because the salt concentration will adversely affect the plants.
  5. Nitrite Poisoning.

A new aquaponics system is more vulnerable to nitrite poisoning, especially when they are not yet correctly colonized by beneficial bacteria. However, nitrite poisoning is not 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.

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 within their range.
  • Remove uneaten fish food and clean the fish tank.
  • Ensure that the tank has enough aeration or add an extra aerator to the system.
  • 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 as salt does not evaporate, be careful to note down when and how much salt you have added to your tank.


Nitrite Poisoning in Aquaponics
3. Fish Stress

Fish stress is the physiological response of the fish when they live in poor conditions. Stress alone will not kill the fish, but they will develop diseases that might kill them if they are stressed for an extended period. So it is better to avoid fish stress as much as possible and know the factors that can cause fish stress.

Causes of Fish Stress:

  • Overstocking.
  • Incorrect temperature. 
  • High level of ammonia, nitrite, or toxins in the system.
  • The pH level in the system is out of range.
  • Low dissolved oxygen.
  • Inappropriate feeding.
  • Poor fish handling.
  • Noise or light disturbance.
  • Bullying companions in the fish tank.

Symptom of Fish Stress:

  • Poor appetite
  • Unusual swimming behavior.
  • Rubbing or scraping at the side of the tank, piping at the surface.
  • Red blotches and streaks.
  • Physical injuries.
  • Fins are clamped close to their bodies
  • Fast breathing
  • Erratic behavior

Treatment of Fish Stress

Salt is also used to treat fish stress in aquaponics. Fish react to stress by excreting minerals into the water. When this condition persists for a long time, salt loss can be fatal for the fish. Adding salt to the water will increase their survival rate because increasing the water salinity will reduce salt excretion and stress to the fish. The recommended salinity level for the fish is 0.5-3 ppt. Keep in mind that adding too much salt can hurt some systems’ plants.

Fish Stress


Most of the causes of fish diseases in aquaponics are not caused by pathogens but are mainly related to the water quality or toxicity in the system. That is why regular monitoring should be implemented in every aquaponics system to ensure that the water quality parameters are at their optimum levels. So take time to observe and monitor the fish in your system to ensure that your system is running smoothly.  


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