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Acute and Chronic Toxicity of Nitrate to Early Life Stages of Zebrafish—Setting Nitrate Safety Levels for Zebrafish Rearing
May 25, 2015
7:56 pm
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BillT
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This paper provides empirically based guidelines for acceptable nitrate levels at different early life of zebrafish.

Tolerance varies with age. It will most likely also vary across sps due to their adaptations to different environments, but these numbers may provide ideas for other species.

In mg/L (ppm), the levels are:

embryo (unhatched egg):    1450 mg/L

newly hatched larvae (round yolk, negatively buoyant, laying around):    1855 mg/L

swim-up larvae (larvae that are working their way to the surface to get a air bubble to help initiate the inflation of their swim bladder):    1075 mg/L

larvae (swim bladder inflated, largely done relying on yolk for nutrition, searching and eating small prey):    200 mg/L

 

Since its not open access only the abstract is freely available, but the results are there.

abstract

Bill Trevarrow [email protected]
May 26, 2015
6:32 pm
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Byron Hosking
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I am not a biologist, but I would certainly seriously question the application of these conclusions long-term.  

NO2-N is nitrate as nitrogen, while NO3 is simply nitrate.  Test kits used by aquarists (like the API) generally measure the latter.  To convert NO3-N to NO3, one multiplies by 4.42.  So 10 mg/l of NO3-3 equates to roughly 40 mg/l NO3.  The numbers in the abstract are NO3-N.  And mg/l is basically ppm, which is the more common measurement unit for aquarists.  [The former is just so we are all on the4 same page.]

In the USA, nitrate in drinking water is required by law to be no higher than 10 mg/l (ppm), or 40 ppm NO3.  Levels above this have detrimental effects on humans, especially for pregnant women and children.

Dr. Neale Monks has advised that nitrates should never be above 20 ppm for any tropical fish, and preferably lower.  He has written that all species of cichlids appear to develop problems with nitrates at 20 ppm or above long-term.  On the cichlid site, they suggest that nitrate above 20 ppm may well cause Malawi bloat.  I would assume these people are referring to NO3.

The "lowest" nitrate level this abstract gives is 200 ppm NO3-N, which would be 800 ppm with our tests of NO3.  I am not going to pay good money to see this entire paper, most of which I probably wouldn't fathom anyway, but the long-term application of nitrates at the unbelievable level they advocate cannot be safe for fish.  Something may be flawed with their reasoning, or I'm not understanding it?

Byron.

Byron Hosking, BMus, MA Vancouver, BC Canada
May 27, 2015
2:52 am
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BillT
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Sounds like you are confusing adult tolerances with the embryonic, larval or prejuvenile tolerances.

Early stages of fish have different and higher sensitivities to nitrate because their biology is different.

 

Dr. Neale Monks has advised that nitrates should never be above 20 ppm for any tropical fish, and preferably lower.  He has written that all species of cichlids appear to develop problems with nitrates at 20 ppm or above long-term.  On the cichlid site, they suggest that nitrate above 20 ppm may well cause Malawi bloat.  I would assume these people are referring to NO3.

I am betting that this statement is all about adult tolerances, not those of embryos or larvae.

Generally I don't like blanket statements concerning different fish species and different stages of life. There is to much variability.

More specifically, many species have different tolerances. Adult Tilapia, for example, can tolerate ammonia levels up to 2 ppm. Zebrafish larvae have been successfully raised in 0.18 ppm free ammonia (article).

General guidelines may provide a large safety margin for hobbyists but are probably pretty inaccurate for raising larvae and could result in a less than optimal use of your resources if you mistakenly tried to meet unnecessarily strict conditions.

Bill Trevarrow [email protected]
May 27, 2015
5:57 pm
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Byron Hosking
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Yes, I was thinking adult tolerances, as we are aquarists and interested in the effect of nitrates on our tank fish.  Usually it is fry that are said to be more sensitive to such toxins, so the natural inference here would be that high nitrate poses no threats.  Something I cannot accept.  But the numbers in this study are so astronomical I would seriously question things.

Byron Hosking, BMus, MA Vancouver, BC Canada
May 27, 2015
6:18 pm
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BillT
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Surprisingly to me also, recently, experiments have shown the high tolerance of young zebrafish stages to these water quality parameters.

Not widely known outside of the lab though.

Bill Trevarrow [email protected]
May 27, 2015
6:31 pm
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BillT
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I have two thoughts on why this might be:

1) The fish's biology is vastly different at early stages. At least up to swim up stages, gill function is probably not important for gas transfer, as the oxygen probably goes right through the skin. Some mutant fish can even develop through these stages without blood cells.

2) The young stages should be adapted to the situations in which they might find themselves. Eggs might be adapted to living buried in muck, where they could avoid parental predation. This might involve exposure to higher levels of nitrogenous compounds. If they could not tolerate these conditions, those eggs would not survive.

Bill Trevarrow [email protected]
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