Ammonia and Nitrite

Nitrogenous wastes can accumulate to potentially toxic levels in intensive shrimp ponds. Ammonia is excreted by shrimp and is also generated by aerobic and anaerobic bacteria in the pond environment. Bacterial metabolism changes ammonia into nitrite and nitrite into nitrate. These bacteria require aerobic (oxygenated) conditions. When anaerobic conditions prevail, nitrite and ammonia are formed in the nitrogen cycle. Thus, the presence of oxygen has a marked effect on the nitrogen cycle in organically rich shrimp ponds, mainly through its effect on bacterial breakdown.

Direct shrimp toxicity data are difficult to interpret for ammonia and nitrite.  Conflicting data
exist in the literature and probably reflect differences in experimental conditions for the various studies. Generally, safe levels for un-ionized ammonia may be in the range of 0. 1 to 0. 5 ppm for nursery and pond grow out. Safe levels for nitrite may be in the range of 0. 1 to 1 ppm.

In addition, nitrogen buildup in the pond environment may be an important indirect factor for

acterial disease. A nitrogen-rich environment may provide a selective advantage to certain groups of marine Vibrio spp. (e.g., the urease positive strains) that are more likely to cause infections in shrimp.

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