Managing High Nitrite (NO₂⁻) in Shrimp Ponds
By Dr.Wiphada Mitbumrung, Ph.D. Applied Marine Biosciences — Thu Apr 09 2026
In shrimp farming, nitrogen management is one of the most critical factors affecting shrimp health and survival. While ammonia is widely recognised for its toxicity, nitrite (NO₂⁻) is equally dangerous and often underestimated. The primary source of nitrogen in shrimp ponds comes from feed input. Uneaten feed, feces, and other organic matter from cell debris and metabolic waste accumulate in the pond and undergo decomposition, releasing nitrogen into the system. This nitrogen is transformed step by step through the nitrogen cycle, starting from organic matter to ammonium (NH₄⁺), then to nitrite (NO₂⁻), and finally to nitrate (NO₃⁻). These processes are driven by nitrifying bacteria that help maintain water quality stability.
Problems arise when the system becomes imbalanced and the reaction rates between each step are not aligned. In many cases, organic matter decomposes rapidly, producing high levels of ammonium, which is then quickly converted into nitrite. However, the final step, where nitrite is oxidised into nitrate, may proceed more slowly. This imbalance causes nitrite to accumulate in the water. When nitrite levels exceed 0.3 ppm, it reaches a risk level that can significantly stress shrimp. Even at lower concentrations, prolonged exposure can negatively affect shrimp performance. Nitrite is harmful because it interferes with the shrimp’s ability to transport oxygen in the haemolymph. Although dissolved oxygen levels in the water may appear adequate, shrimp are unable to efficiently utilise it. As a result, shrimp become weak, show reduced feeding activity, experience slower growth, and face increased risk of mortality.
Managing high nitrite levels requires restoring balance in the nitrogen cycle and promoting the efficient conversion of nitrite to nitrate. One of the most important actions is to increase aeration. The bacteria responsible for oxidising nitrite to nitrate are chemoautotrophic nitrifying bacteria, which are strictly aerobic and require a high supply of oxygen to function effectively. Increasing aeration and improving water circulation enhances their activity and accelerates nitrite removal.
At the same time, it is important to reduce further nitrogen input into the system. Temporarily stopping feeding for one day, or significantly reducing feed, helps limit the addition of new organic waste. This allows the microbial community to process the existing nitrogen load more effectively. Supporting microbial activity can also help stabilize the system. Heterotrophic bacteria are especially useful because they are effective at degrading organic matter into ammonia, which helps reduce the accumulation of waste in the pond. In addition, heterotrophic bacteria can also assist in nitrogen oxidation processes similar to those carried out by nitrifying bacteria, although they do so less efficiently and more slowly. While autotrophic nitrifying bacteria are more specialized in converting ammonia to nitrite and nitrite to nitrate through the nitrification pathway, they are slow-growing and difficult to increase quickly in the pond. By contrast, heterotrophic bacteria can multiply rapidly and provide valuable short-term support during periods of imbalance, helping to improve overall microbial activity and reduce pressure on the system.
As the pond condition improves, farmers will often observe an increase in ORP, indicating a more oxidative and stable environment. At the same time, nitrite levels will begin to decrease over the following days. High nitrite is therefore not just a water quality issue, but a clear signal of imbalance in the nitrogen cycle. By improving aeration, reducing waste input, and supporting microbial processes, farmers can effectively bring the system back into balance and maintain a healthier environment for shrimp growth.