Are Koi Wusses? Part VII - Nitrite

 We know that the product of Ammonia oxidation is Nitrite. This is also toxic to Carp (Koi) at very low levels. Any reading greater than 0.06 mg/L is considered lethal. This level is roughly equivalent to one drop in a pint of water.

Like Ammonia, Nitrite toxicity is influenced by both pH and temperature .In one study, two (2) different groups of Carp (Cyprinus carpio) were subjected to nitrite levels of 0.0667 for 48 hours at temperatures of 14C/57F and 20C/68F. The mortality rate for each group was 30% and 51% respectively.

In addition toxic effects of nitrate are more likely at low dissolved Oxygen levels.

Nitrite toxicity occurs as Nitrite enters the fish by way of the gills and passes into the circulatory system (Perrone, 1977). Toxic effects of nitrite include oxidation of hemoglobin to methemoglobin, a form incapable of binding molecular oxygen (Brown and McLey, 1975).

Fish with methemoglobin can be detected by the colour of the blood and also by brown colour of the gills (Brown Blood Disease). As nitrite rises, the fraction of methemoglobin in the blood reduces the oxygen carrying capacity of the blood (Cameron, 1971). Fish with elevated levels of methemoglobin may suffer from anoxia (Tomasso, 1981). . Since methemoglobin does not transport oxygen, asphyxiation is the principal reason fish die from nitrite poisoning

Nitrite is less toxic than Ammonia, but the toxic effects of Nitrite occur much more rapidly than those of  Ammonia.

Chloride is used to “treat’ Nitrite toxicity. This may be Sodium Chloride (Pond Salt) or Calcium Chloride, which is more expensive. The chloride portion of salt competes with nitrite for absorption through the gills .If problems with Nitrite levels exist, maintaining at least a 10 to 1 ratio of chloride to nitrite in a pond effectively prevents nitrite from entering Koi.  As a general rule, 50 to 100 ppm chloride in pond waters will guard against high spikes of nitrite concentration. 1,000 ppm of salt is equal to a 0.1% level. (Note: This should be done only if a Nitrite problem is detected. Maintaining salt levels will over time result in parasites and other pathogenic organisms adapting to these salinity levels making them harder to control through the normal “Salt Treatments” .Use Salt only as a temporary fix. Adequate bio-filtration (bioconversion) will maintain safe nitrite levels.)

It should be noted that Carp(Koi) can survive ‘Brown Blood Disease’ if treated in time, but with a resulting lowered immune system making them more susceptible to other infections that can occur for up to 3 weeks after the “Brown Blood Disease’ is cured.

Carp(Koi), though highly adaptable are as susceptible to Nitrite poisoning and it’s effects as any other fish
Nitrite level is probably the most important water quality parameter because it’s effects occur rapidly and should be tested for frequently along with Ammonia.

Next Post:  Nitrates