Ammonia vs Nitrites

kreblak

kreblak

FDA approval pending
Mar 13, 2003
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This may seem like a moot question, but which is more toxic to fish, ammonia or nitrites? I ask because I was reading about a study done in Japan at a commercial tuna farm. There, disease can wipe out their entire profit margin, so they maintain strict quarantine tanks. The study showed that 95% of fish casualties occured about 3 to 5 days into the quarantine. 3 to 5 days into the quarantine would be when ammonia levels would be approaching 3 or 4 PPM, and nitrite levels would begin rising above zero (assuming the q tank had not been recently occupied).

So, are the ammonia levels causing the fatalities, or the increasing of nitrite levels, or is it a little of both?
 
It would be very surprising if a commercial facility did not use cycled tanks so I would not think that increasing ammonia or nitrite to be the cause of the death.

Having said that, which is more toxic? They both just as toxic but it depends on the specifics.

Ammonia toxicity is pH dependant. The higher the pH the more toxic Ammonia is (because of the ammonia/ammonium balance). Ammonia toxicity is also not reversable, so once the damage is done, it is done.

Nitrite toxicity on the other hand is not pH dependant and even small concentrations are toxic (in the same way Carbon monoxide is toxic to humans). However nitrite toxicity is reversable if treated early. This can be done by putting the fish into a nitrite free environment or you can add chemcials such as methylene blue which are known to reverse nitrite toxicity. But again, if organ damage has already occured then it is too late

The best answer is fish should not be exposed to either in any measurable concentrations
 
The way I know it is that ammonia (not including ammonium, when the pH is more acidic than neutral) is more toxic in SW tanks, but nitrite is more toxic in FW. I'd like to know if this is right.
 
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