A Silent Threat to Fish and Shrimp

Elevated ammonia nitrogen in water is one of the most common and dangerous water quality problems in aquaculture and natural aquatic environments. Although ammonia exists in two forms—ionized ammonium (NH₄⁺) and unionized ammonia (NH₃)—it is the unionized fraction that is highly toxic to fish and shrimp, even at very low concentrations.

When ammonia levels exceed safe limits, the harmful effects begin quickly. The most immediate damage occurs to the gills. Ammonia causes physical injury to gill tissues, leading to inflammation, thickening of the gill epithelium, and reduced oxygen exchange. Affected fish and shrimp often gasp at the water surface, appearing restless or lethargic.

Inside the body, ammonia interferes with key physiological processes. It enters the bloodstream and disrupts the transport and release of oxygen by destroying red blood cells or impairing hemoglobin function. As a result, the animals suffer from internal suffocation even if the surrounding water contains enough oxygen.

The nervous system is another primary target. Ammonia easily crosses the blood‑brain barrier and affects brain metabolism. It can cause hyperactivity, erratic swimming, loss of balance, convulsions, and eventually coma. In shrimp, exposure often leads to reduced feeding, poor molting, and abnormal coloration.

Chronic exposure to moderately high ammonia—even without immediate death—seriously weakens the animals. Growth slows down, feed conversion becomes inefficient, and immune function drops. Fish and shrimp become far more susceptible to bacterial and parasitic diseases. Reproductive performance may also decline, with lower egg production and larval survival.

In practical terms, the most sensitive species are salmonids (trout, salmon), many warm‑water fish like catfish and carp, and all species of shrimp and prawns. Young juveniles are more vulnerable than adults.

Prevention and control are the only solutions. Regular water exchange, proper aeration, biofiltration (nitrifying bacteria), and avoiding overfeeding can keep ammonia within safe ranges. Once poisoning occurs, immediate actions such as water change, salinity adjustment (in shrimp ponds), and reducing pH to lower the proportion of toxic NH₃ can provide relief.

In summary, ammonia nitrogen is not merely a chemical indicator—it is a direct and potent poison to fish and shrimp. Protecting aquatic life starts with understanding this silent threat and maintaining ammonia at near‑undetectable levels.