VPP 322: Aquatic Animal Diseases, Health Care and Management (1+1)

NITRITE POISONING

• The most circumstances causing ammonia poisoning can also leads to nitrite poisoning. In a newly established aquarium, nitrite buildup usually occurs after ammonia has peaked. This is because the Nitrobacter bacteria that convert nitrite to nitrate require time to become active just like the bacteria that convert ammonia to nitrite. In ponds, nitrite poisoning is common in fall because the temperature optima of Nitrosomonas and Nitrobacter are different.

Clinical signs of nitrite poisoning

• Nitrite is actually transported across the gills, where it enter the blood stream and oxidize hemoglobin to a methemoglobin. Methemoglobin cannot transfer the oxygen efficiently, so tissue are deprived of oxygen. While oxygenated Hb is red, MetHb is brown. So fish with nitrite poisoning often have pale tan or brown gills. Methemoglobin concentrations of 25% to 40% cause grossly visible chocolate brown blood and pale tan–to-brown gills. Fish with anaemia may also have pale gills but with a red tinge. Fish with severe (i.e., 80% or greater) methemoglobinemia are dyspenic even with adequate oxygen.
• Behavioral changes noted with nitrite poisoning are characteristic of hypoxia, including lethargy and congregating near the water surface. Fish with nitrite poisoning should be disturbed as little as possible, since even minor exertion may cause acute mortality.

 

Brown discolouration of gills in nitrite poisoned fish

Source:gardenofeden.com

Diagnosis of nitrite poisoning

• It requires measuring the metHb concentration in the blood combined with measuring the nitrite concentration in water. However, routine clinical diagnosis of nitrite toxicosis relies on measuring nitrite levels. This has limitation, since fish vary greatly in susceptibility to nitrite poisoning.

Treatment of nitrite poisoning

• Aquaria
  • 25 - 50% water change (daily to weekly, depending on nitrite concentration)
  • Add nitrifying bacteria
  • Add chloride
  • Setup biological filteration
  • Decrease density
  • Reduce temperature
  • Reduce feeding
• Ponds
  • Add chloride
  • Maintain highest DO possible