Ammonia poisoning

AMMONIA POISONING

  • Ammonia poisoning is one of the most common water quality problems diagnosed in aquaculture. Ammonia is the primary nitrogenous waste product of fish and also originates from decay of complex nitrogenous compound. Ammonia poisoning leads to acute mortality, but most often it present as a sub-lethal stress.

Causes of ammonia poisoning

  • Overcrowding, recent medication or other chemical added, newly established aquarium, aquarium gravels recently washed or other filters recently cleaned, failure of biological filters, recent algal crash in pond, reduced water flow in race ways and hyperexcitability are some of the causes for ammonia poisoning.

Clinical signs of ammonia poisoning

  • Ammonia toxicity can be caused by behavioural abnormalities such as those that occur in mammals, including hyperexcitability. Fish often stop feeding. Chronic ammonia poisoning has been associated with hyperplasia and hypertrophy of gill tissue, although it is unclear as to whether this nonspecific pathology is directly due to ammonia poisoning or rather to other aspects of poor water quality that frequently accompany chronically high ammonia.
  • The precise mechanism of ammonia poisoning in fish is unknown, but high aqueous ammonia increase blood and tissue ammonia levels, causing elevated blood pH, osmoregulatory disturbance, increased tissue oxygen consumption and decreased blood oxygen transport. Chronic ammonia poisoning decreases growth and disease resistance.

Diagnosis of ammonia poisoning

  • Ammonia level is determined using commercially available kits. The kits measure the nitrogen present as ammonia, also known as total ammonia nitrogen (TAN), an ion -specific electrode can also be used to measure ammonia.
  • Ammonia is present in two forms, ionized and unionized. Unionized ammonia (UIA) is toxic to fish, while ammonium is much less toxic. The amount of UIA in water depend mainly upon the pH and also on temperature and salinity. High pH and temperature and low salinity favour the presence of UIA.

Treatment of ammonia poisoning

  • Aquaria
    • Ammonia levels can be reduced with frequent water changes. But, in a long –established tank, the clinician must be careful not to cause environmental shock. Adding zeolite is a safe and effective way of reducing ammonia quickly. However, zeolite’s efficiency decreases with increased salinity. Reducing the pH will reduce the percentage of ammonia that is present as NH3. For every one unit decrease in pH, there is a 10 fold decrease in UIA.
    • In the established tank, ammonia poisoning rises when more fish are in that tank than the biological filtration can handle. In this case, either some fish must be removed or more filtrations must be added.
  • Pond, cages, flow-through systems
    • It is advisable to feed not more than 110 kg of feed /ha/day to avoid ammonia accumulation in catfish ponds.
    • In flow through systems, reducing stocking densities or feeding rates or increasing water flow is the most common treatment for ammonia build up.
Last modified: Friday, 16 September 2011, 11:46 AM