Coastal Aquaculture and Mariculture (2+1)

Unit 4 - Water and soil quality management

4.1.2.f. Nitrite and Nitrate

Nitrite

• Nitrite like ammonia is toxic to fish.
• Nitrite levels in fish ponds typically range from 0.05 to 5 mg/L, probably due to reduction of nitrate under anaerobic conditions.
• The toxicity of nitrite is due to its effect on oxygen transport and tissue damage.
• Fish deaths increase when low dissolved oxygen is coupled with higher nitrite concentrations.
• DO levels should be higher than 6 mg/L when fish are affected by nitrite toxicity.
• At higher levels of chloride the toxicity of nitrite is reduced. Hence nitrite toxicity in seawater is not as serious as in freshwater systems.

Nitrate

• Nitrates are the least toxic of the inorganic nitrogenous compounds.
• The effects on aquatic animals is similar to nitrate having to do with osmoregulation and oxygen transport, but the concentrations at which fish get affected are much higher.
• Nitrates are more of a problem in recirculatory systems and the problem is controlled with daily water exchanges.