Could managing ammonia in fish ponds benefit productivity?

Ammonia concentration can have a direct effect on water quality, especially in ponds fed with high-protein aquafeed. Water quality management is one of the essential management tasks in aquaculture farming, and daily or routine water quality measurement and recording have become some of the critical success factors in ammonia control in aquaculture farming. When optimum water quality is being maintained,  the better the growth performance that the farmers will reap. Based on the water quality record, farmers can take necessary corrective actions to improve the pond water quality, including the application of some chemicals, probiotic or mechanical aerations or water exchange. The water quality parameters monitored depend primarily on the culture system and sensitivity of the aquatic animals to particular water quality parameters. Many parameters can directly affect ammonia’s toxicity.

Water quality parameters measured by most farms are:

• Dissolved oxygen (DO)
• pH
• Temperatures
• Total ammonia nitrogen
• Salinity

Effects of ammonia in pond aquaculture  

Among all the water quality parameters, ammonia is considered one of the toxic substances that requires more careful monitoring within the culture system, as it can cause stress and damage to gills and other tissues. Ammonia is a major waste product of aquatic animals, resulting from the breakdown of feed and other organic matter that is excreted into the water. Ammonia can occur in two forms: unionized form ammonia (UIA)(NH₃⁺) and ionized ammonia (NH₄). Unionized ammonia is toxic to fish and all aquatic animals, and its concentration can be elevated by increases in pH and temperature (Table 1). pH has a greater impact on ammonia toxicity compared to temperatures, so it is imperative to test pH while measuring the total ammonia nitrogen (TAN) level to understand the actual risk to aquatic animals.

Ammonia in water is dynamic during the day and throughout the whole culture period. Farmers seldom report cases of high mortality caused by high ammonia levels, but they cannot be ignored, as these hidden performance indicators could cause a severe financial loss. These consequences include:

• Reduced appetite
• Increased susceptibility to bacterial infections
• Reduced growth rate
• Poor feed conversion ratio (FCR)

Safe concentrations for long-term exposure are around 0.015–0.045 for coldwater species and about 0.05–0.15 for warm water and marine and shrimp. In the actual farming environment, aquatic animals are not usually exposed to extremely high ammonia levels for extended periods. Therefore, understanding and applying the safe concentration level for long-term exposure to ammonia would be the most practical approach for farmers. TAN must be kept low throughout the culture period to optimize the performance.

Table 1: LC50 concentration

(Bloyd 2018, reported the LC50 concentrations (concentrations required to kill 50% of test animals)

Managing ammonia in pond aquaculture

Using water testing kits is a well-established standard practice for measuring the TAN at farm level. This is a process completed once per week. However, common misunderstandings on the control of ammonia, and management practice requires further attention and clarification. Practically, measuring ammonia only once a week should be sufficient. But, bear in mind that where there is higher biomass (higher stocking density), or at the growing stage or near the harvest stage on the culture cycle where the feeding rate is high, there are possibilities of high nitrogen input into the system caused by uneaten feed and/or more feces from growing animals. Ideally, it is recommended to take a water sample and TAN test twice per week during the last phase of the growing stage or near the harvest stage. This helps in monitoring whether TAN is in the right range and managing the feeding rate accordingly. During the culture cycle, when the pond water plankton is not stable, allowing for a high fluctuation of pH in the pond water, the TAN testing should be applied to check the UIA level. UIA will increase along with the pH in pond water. It is essential to perform the TAN test along with a pH test for the most accurate results.  

There are several ways to rectify the high TAN in the waters:

• Water exchange is often the preferred choice if there is abundant clean and treated water available. However, high daily water exchange is not a sustainable practice, and it could lead to high-risk exposure to the pathogen, especially under the disease threat of surrounding farms.
• Increased aeration is believed to accelerate the diffusion of ammonia gas from pond water to the air. However, some research has shown that this can, in fact, increases ammonia concentration in intensive systems.
• Reduce feeding rate
• Routine application of probiotics in pond water could help. However, when there is an ammonia spike, this probiotic may not act rapidly enough to reduce the ammonia level.
• Zeolite (only applicable in freshwater).

How to reduce ammonia levels in fish ponds

In nature, the Yucca Schidigera plant grows in the desert. Its bioactive component can absorb or bind the ammonia found in water, reducing ammonia pollution (Figure 1). De-Odorase® from Alltech is a product containing yucca plant extract. Traditionally in agriculture, De-Odorase is added into animal feed to keep manure odor and ammonia at levels conducive to maintaining respiratory health. This creates a healthier environment, not only for the animal but also for the producer.

Figure 1: Yucca trees at Alltech Serdan, Mexico.

De-Odorase can be applied directly to the pond water in aquaculture to effectively reduce ammonia levels in the water with no adverse effect on the aquatic animal. This is widely accepted and considered as a safe product for aquaculture farmers, who can routinely apply it to the water to maintain safe ammonia levels. Local trials in Indonesia have demonstrated that De-Odorase to reduce the TAN in water within 1.5 hours, but also maintain this reduced level long-term (Figure 2).

Figure 2: Application of De-Odorase (0.3ppm) in Asian Seabass Hatchery

The correct dose and proper management practices are the essential elements in achieving lower TAN levels. The right dose of De-Odorase contains sufficient yucca extract to ensure the rapid binding of ammonia without delay. The correct application requires adding the right ratio of water with the Deodorase powder to create the correct volume of yucca solution to use in all areas of the pond. However, it is important to note that De-Odorase is not just a one-time solution for solving all issues relating to ammonia. It is equally crucial to improve management practices, such as reducing the feeding rate and turning on the aeration. If normal feeding is resumed before reaching a safe ammonia level, the levels will rise again. The uneaten feed, due to the reduced appetite of the aquatic animals induced by high ammonia levels, will contribute to bringing the ammonia back to the aqueous system.   

Prevention is always better than treatment, and this concept is applied to water quality management in aquaculture too. Maintaining a well-managed water quality maintenance program will ensure the ammonia levels are consistently at a safe level for the aquatic animals, while also providing a sustainable solution for long-term benefits. Optimal water quality parameters and their variations across the culture cycle should be understood, and a management action plan should be in place to achieve increased productivity.

To find out how to measure the ammonia levels on your farm, please email aquasolutions@alltech.com, and we will put you in touch with one of your local representatives.