Nitrite Poisoning
Disease Type: Environmental

Description
Nitrite poisoning follows closely on the heels of ammonia as a killer of aquarium fish. Just when you think you are home free after losing half your fish to ammonia poisoning, the nitrites rise and put your fish at risk again. Anytime ammonia levels are elevated, it is a safe bet that elevated nitrites will soon follow. To avoid nitrite poisoning, test when settng up a new tank, in established tanks when adding new fish, when the filter fails due to power or mechanical failure, and when treating sick fish with medications.

Symptoms

  • Fish gasp for breath at the water surface
  • Fish hang near water outlets
  • Fish is listless
  • Tan or brown gills
  • Rapid gill movementAlso known as ‘brown blood disease’ because the blood turns brown from a increase of methemoglobin. However, methemoglobin causes a more serious problem than changing the color of the blood. It renders the blood unable to carry oxygen, and the fish can literally suffocate even though there is ample oxygen present in the water. Different species of fish tolerate differing levels of nitrite. Some fish may simply be listless, while others may die suddenly with no obvious signs of illness. Common symptoms include gasping at the surface of the water, hanging near water outlets, rapid gill movement, and a change in gill color from tan to dark brown. Fish that are exposed to even low levels of nitrite for long periods of time suffer damage to their immune system and are prone to secondary diseases, such as ich, fin rot, and bacterial infections. As methemoglobin levels increase damage occurs to the liver, gills and blood cells. If untreated, affected fish eventually die from lack of oxygen, and/or secondary diseases.
  • Treatment
  • Large water change
  • Add salt, preferably chlorine salt
  • Reduce feeding
  • Increase aerationThe addition of one half oz of salt per gallon of water will prevent methemoglobin from building up. Chlorine salt is preferable, however any aquarium salt is better than no salt at all. Aeration should be increased to provide ample oxygen saturation in the water. Feedings should be reduced and no new fish should be added until the tank until the ammonia and nitrite levels have fallen to zero. Nitrite is letal at much lower levels than ammonia. Therefore it is critical to continue daily testing and treatment until the nitrite falls to zero.
  • Prevention
  • Stock new tanks slowly
  • Feed sparingly and remove uneaten food
  • Change water regularly
  • Test water regularly to catch problems earlyThe key to elminating fish death is to avoid extreme spikes and prolonged elevation of nitrites. When starting a new tank, add only a couple of fish initially and do not add more until the tank is completely cycled. In an established tank, only add a couple of new fish at a time and avoid overstocking. Feed fish small quantities of foods, and remove any food not consumed in five minutes. Clean the tank weekly, taking care to remove an dead plants or other debris. Perform a partial water change at least every other week, more often in small heavily stocked tanks. Test the water for nitrite after an ammonia spike has occured as there will be a nitrite increase later.
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    ~ Shirlie Sharpe