Hi all, I think these are very relevant questions, and this is discussed, to some degree in the <"
Best way to cycle a second...">.
I think the answer is that nitrification is likely to occur at lower levels of dissolved oxygen than was originally thought, mainly because the
<"organisms involved are Archaeae">. The work on Aquarium filters is reported in <"
Aquarium Nitrification Revisited: Thaumarchaeota Are the Dominant Ammonia Oxidizers in Freshwater Aquarium Biofilters">.
The real problem is that, most of what, we thought, we knew about the ammonia oxidising organisms (AOO), isn't actually true for aquariums. Earlier work (and bacterial supplements) utilised Nitrosomonas, Nitrobacter and Nitrospira based on work originally done on sewage treatment etc. Subsequent research has shown that only Nitrospira (which was thought to convert nitrite (NO2) to nitrate (NO3)) is present, and that Nitrospira can also <"directly oxidise ammonia (NH3) to NO3">.
Doctor Hovanec's comments on changes in our knowledge about nitrifying organisms are here: <"
Bacteria revealed">, and it is well worth a read. His scientific papers are
<"here">, and his products page is here: <"
DrTim's Aquatics">, where you can buy the latest incarnation of
<"One and Only: Live Nitrifying Bacteria">, which doesn't need to be refrigerated. I'm not sure any-one will know. You can make assumptions based on the natural habitat of fish, rheophilic fish from cooler waters are likely to be the most vulnerable to low oxygen levels. There is more discussion in <"
Aeration and dissolved oxygen....">
Due to the relationship between temperature and gas solubility (as temperature rises solubility falls) warm water that is 100% saturated with oxygen may not not contain enough dissolved oxygen (in mg/l) to sustain some fish. There is a chart to work out the relationship between temperature and DO in <"
Twinstar..what is it: page 34">.
There are minimum figures for the organisms grown in commercial aquaculture, you could assume that Atlantic Salmon (
Salmo salar) would be about the most sensitive, and it needs <70% DO levels (at 16oC) for growth, and the hypoxia tolerance threshold is 47% O2.
cheers Darrel