Is Aquaponics Cruel To Fish?

Aquaponics has been touted as a sustainable way to raise fish simultaneously and grow water-borne vegetables. This practice seeks to maximize the symbiotic relationship between fish and plants—the fish creating waste that nourishes the vegetables while the plants filter the water for the fish. But is aquaponics cruel to fish? 

Aquaponics is not cruel to fish as it doesn’t deliberately harm the fish in the ecosystem. However, many problems may arise in aquaponics, so it’s important to keep a close eye on your fish to ensure they’re not harmed or under stress.

You should have a successful and cruelty-free aquaponics environment if you follow the best practices. Keep reading to learn more about how aquaponics could harm your fish and what you can do to prevent it.

Challenges to Fish Well-being in Aquaponics

Unless the fish are being raised for the express purpose of killing and eating them, you don’t need to harm them.

However, there are many ways aquaponics fish could be hurt if you’re not careful:

Water Contamination

One of the main tenets of aquaponics is that the nitrifying bacteria in the grow beds and the plants should effectively filter the water in the tank. The problem is that plants can’t filter all of the fish waste, which can contaminate the water and make it toxic for fish. 

Even if your aquaponics tank looks crystal clear, there may be waste residue in the water that can harm your fish.

A contaminated fish tank could result in diseases like:

  • Bacterial infections
  • Parasite infections
  • Fish fungus

Aquaponics tanks can get easily contaminated if not cared for properly. The plants alone won’t filter all of the water in your tank, so you should take additional measures to ensure a safe environment for your fish.


Fish stress can lead to severe illnesses in fish that could ultimately kill them. Stress happens due to poor water conditions that could result in a less than ideal situation for your fish.

Fish stress could lead to:

  • Loss of appetite
  • Scale problems like red blotches
  • Physical injuries
  • Erratic swimming and unusual behavior

Aquaponics tanks are notorious for having overcrowding issues. Since the amount of waste needed to nourish the plants is quite high, aquaponics farmers are pressured into adding an unsanitary amount of fish into small tanks.

The rule of thumb is that you need 1 gallon (4.55 L) of water per inch of fish. This can be troublesome for aquaponics tanks as the larger the fish population, the more plants will be needed to filter the water. However, the more plants you have, the more fish you’ll need, so this is an unsustainable issue without a simple solution. 

Nitrate Poisoning

Nitrate poisoning is very common in aquaponics tanks. Although live plants do use nitrate and remove a lot of it from the water, aquaponics plants can’t remove enough nitrate quickly enough to keep the levels safe for fish. You should try to keep your nitrate levels below 20 ppm at least, but ideally under 10 ppm

If your fish are experiencing nitrate poisoning, they may be showing some of the following symptoms:

  • Laziness or lethargy
  • Loss of appetite
  • Rapid or erratic gill movement
  • Laying on the bottom of the tank

If you think your fish might be suffering from nitrate poisoning, the first thing you should do is test the water for nitrogen levels. If the levels are above 30 ppm, you’re probably dealing with fish suffering from high nitrate levels.

Preventing Harm to Aquaponics Fish

If you want to keep your aquaponics fish happy and safe, you should take extraordinary care of them and their environment. The hydroponics plants in your tank won’t be enough to keep your fish’s environment safe for them.

Try the following to ensure your fish’s safety and comfort:

Regular Water Testing

The most important thing you can do is test the water quality regularly. A complete water test kit can help you test for the most important water parameters, such as pH, ammonia, nitrite, and nitrate. By testing often, you’ll catch a problem with your water before it becomes an issue for the fish.

Selecting Quality Fish

Purchasing healthy and high-quality fish from trusted fisheries will increase the chances of keeping your fish healthy and happy. You should also make sure to purchase the fish species that are best suited for your aquaponics system

If you’re unsure which fish species are best for your aquaponics tank, watch the following YouTube video for a detailed breakdown of the best species for aquaponics:

Salt Baths for Fish

Although it sounds fancy, salt baths are essential for maintaining fish health and preventing diseases. Salt baths have been shown to have medicinal benefits for fish and can be a key way to stave off illness.

To give your fish a salt bath, follow the simple steps below:

  1. Make a salt bath in a separate tank or large container with a concentration of 2.20 pounds (1 kg) of salt for every 26.42 gallons (100 liters) of water.
  2. Take your fish out of their aquaponics tank and place them in a salt bath.
  3. Keep your fish in the salt bath for 20–30 minutes, and then transfer them to a lightly salted isolation tank. This isolation tank should only have 0.07 oz (2 grams) of salt per 0.26 gallons (1 liter) of water. Keep your fish in the isolation tank for 5–7 days.
  4. Don’t move any saltwater in when putting them back in the aquaponics tank. Saltwater could damage your hydroponics plants.

For more information on preventing disease in your aquaponics tank, watch the following YouTube video from Aquaponics Revolution.

Final Thoughts

Aquaponics doesn’t have to be cruel to fish as long as the fish are actively taken care of. Contaminated water, poor swimming conditions, and unhealthy nitrate levels could injure the fish, so it’s important to stay on top of water quality and fish health. 

Dr. Moritz Picot

Dr. Moritz Picot is a horticulture enthusiast and the founder of, where he serves as the lead content writer. He established the website in 2022 as a valuable resource for both gardening aficionados and beginners, compiling all the gardening tips he has accumulated over the past 25 years. Alex has a passion for nurturing plants, transforming backyards into inviting spaces, and sharing his knowledge with the world.

Recent Posts