Ammonia is the major toxic component produced continuously by shrimps during culture. It can also accumulate in the water due to the decomposition of organic matter as excess feed, faeces, dead shrimp and dead algae. Ammonia is the main end product of protein catabolism in crustaceans and can account for 60–70% of nitrogen excretion with only small amounts of amino acids, urea and uric acid. Of the nitrogenous compounds, ammonia is the most toxic with nitrite and nitrate being less toxic to shrimp.

Ammonia is the primary excretion product of protein metabolism. In water, ammonia is present in both ionized (NH4+) and un-ionized (NH3) state, with NH3 as the toxic form due to its ability to diffuse across cell membranes. Unionized ammonia is highly toxic to the shrimp and must be removed from the system. The relative proportions of NH3 and NH4+ depend on pH, temperature and to a lesser extent on salinity. Ammonia is nitrogenous waste produced from feed input and microbial decomposition of organic matter in water columns. Shrimp feed is usually high in nitrogen.

In vannamei culture, sometimes only 22 percent of the Nitrogen input is converted to harvested shrimp. 57 percent is discharged into the environment and 14 percent remains in the sediment.

Ammonia Toxicity in Vannamei

• High concentrations of ammonia may affect growth rates and survival, and can in extreme cases cause mortality.
• Ammonia damages the gills and reduces the ability of hemolymph to transport oxygen while increasing oxygen consumption by tissues.
• Ammonia stress could affect a variety of physiological functions including respiration, metabolism, excretion.
• Ammonia in the form of un-ionized ammonia (NH3) is very toxic to aquatic animals and cause impairment of cerebral energy metabolism and damage to gill, liver, kidney, spleen, and thyroid tissue in fish, crustaceans and molluscs.
• Ammonia may also increase the moulting frequency of shrimps. Ammonia is also thought to cause damage to the central nervous system.

Ways to prevent ammonia build-up

• Weekly measurements
• Feeding regimes
• Maintaining alkalinity
• Keeping pH steady
• Managing Salinity and Dissolved Oxygen

If you want to solve the problem of Ammonia, you should do the following:

• Complete a 25% water change and retest after a few hours
• Treat with Ammonia Remover
• Proper feed management
• Continue to regularly test your water