Nitrate myth?

[Barry Tetra]

Is it a myth that nitrates are bad for fish? it seems to me nitrates often get blamed when something goes wrong, even though it could just as easily be bacteria, parasites, or other issues. I keep mine around 60mg/L+ in planted tank and my cardinal tetras are still breeding just fine, I got a batch of fries from that.

 

[GaryE]

It's not a myth, but it is overblown. I recently read an aquarist, a local person, who said every fish disease could be detected with an API test kit. That was foolish, but you could almost be convinced if you read online hobbyists. The cycle is real and important, but a lot of people wear 'cycling goggles' when they look at their tanks. The importance of the cycle can be over applied.

I've seen people describe classic parasite infestations and read responses saying to immediately test the water. It doesn't always make sense...it does no harm but it isn't the problem there.

But nitrates are very bad for fish. It's one of many elements you have to look at when things go wrong. There are different tolerances, as you saw with getting fry from your cardinals ('fries', a fast food, will add to nitrates!).

 

[TwoTankAmin]

Yes nitrates can be a problem.

Kellock, K.A., Moore, A.P. and Bringolf, R.B., 2018. Chronic nitrate exposure alters reproductive physiology in fathead minnows. Environmental Pollution, 232, pp.322-328.

Abstract

Nitrate is a ubiquitous aquatic pollutant that is commonly associated with eutrophication and dead zones in estuaries around the world. At high concentrations nitrate is toxic to aquatic life but at environmental concentrations it has also been purported as an endocrine disruptor in fish. To investigate the potential for nitrate to cause endocrine disruption in fish, we conducted a lifecycle study with fathead minnows (Pimephales promelas) exposed to nitrate (0, 11.3, and 56.5 mg/L (total nitrate-nitrogen (NO3-N)) from <24 h post hatch to sexual maturity (209 days). Body mass, condition factor, gonadal somatic index (GSI), incidence of intersex, and vitellogenin induction were determined in mature male and female fish and plasma 11-keto testosterone (11-KT) was measured in males only. In nitrate-exposed males both 11-KT and vitellogenin were significantly induced when compared with controls. No significant differences occurred for body mass, condition factor, or GSI among males and intersex was not observed in any of the nitrate treatments. Nitrate-exposed females also had significant increases in vitellogenin compared to controls but no significant differences for mass, condition factor, or GSI were observed in nitrate exposed groups. Estradiol was used as a positive control for vitellogenin induction. Our findings suggest that environmentally relevant nitrate levels may disrupt steroid hormone synthesis and/or metabolism in male and female fish and may have implications for fish reproduction, watershed management, and regulation of nutrient pollution.
from https://www.sciencedirect.com/science/article/abs/pii/S0269749117313520

More studies here:
Camargo, J.A., Alonso, A. and Salamanca, A., 2005. Nitrate toxicity to aquatic animals: a review with new data for freshwater invertebrates. Chemosphere, 58(9), pp.1255-1267.
https://www.academia.edu/download/4...Aquatic_Animals_A_Re20160928-15458-l6ojol.pdf

Daniel F Gomez Isaza, Rebecca L Cramp, Craig E Franklin, Simultaneous exposure to nitrate and low pH reduces the blood oxygen-carrying capacity and functional performance of a freshwater fish, Conservation Physiology, Volume 8, Issue 1, 2020, coz092, https://doi.org/10.1093/conphys/coz092

And here is a link to many papers about nitrate toxicity to freshwater fish
https://scholar.google.com/scholar?hl=en&as_sdt=0,33&q=nitrate+toxicity+to+freshwater+fish

 

[seangee]

These are my own observations ...

• Many species can tolerate conditions quite different to their natural habitat. In the long term the only noticeable effect will be a shorter average lifespan. Chances are the fish live a normal healthy life so it would be wrong to say this is cruel or inhumane treatment. Note this is not universally true - there are species that would die very quickly in your 60mg/L water.
• Old tank syndrome is not a mass die off of fish once a particular substance reaches a certain threshold. The die off is most often triggered by a sudden dramatic change in parameters, like when somone feels bad they haven't cleaned their tank in 2 years and does a major clean and changes 50% of the water. Consistency is more important than the exact number.
• Tanks that are reguarly maintained are less likely to contain dangerous levels of pathogens (bacteria etc).

For me the main requirement is to keep my water parameters at the state where I could change all the water without causing an adverse reaction, meaning my tanks contain water that is similar to what I put in if I have to do a large emergency water change. Over time the water parameters drift from the water that we originally put in. The easiest way to control this (at least for me) is with regular substantial water changes. This way I have the confidence that I can change 90% of the water in any of my tanks with no ill effects, or even move all my fish into a brand new tank (but of course that would need cycling!). These water changes also mean that any other stuff that finds its way in is diluted.

FWIW my tap water has nitrate at 50ppm. Before I switched to RO my tanks were never below 60ppm. Yes my fish do live much longer today than they used to - but I can't say that is only due to nitrate levels because of course the hardness is different too.

 

[jaylach]

Nitrates are one of the reasons that regular water changes are needed. In a cycled tank bacteria converts ammonia from fish waste and other sources to nitrites. Other bacteria converts nitrites to nitrates. Sadly nature forgot to make bacteria to get rid of nitrates. Plants DO help but are not a cure-all. Ammonia is the most toxic followed by nitrites. While not as bad as the other two nitrates are still toxic. Just how toxic depends on the fish species. Some species can handle nitrate levels of 40-50 PPM and more but others can not. Take my current favorite species, Panda Garra... A nitrate level of 20 PPM is quickly fatal.

You can get nitrate filters that will remove the crud but water changes are the best as they also dilute other bad stuff.

 

[GaryE]

For me the main requirement is to keep my water parameters at the state where I could change all the water without causing an adverse reaction, meaning my tanks contain water that is similar to what I put in if I have to do a large emergency water change. Over time the water parameters drift from the water that we originally put in. The easiest way to control this (at least for me) is with regular substantial water changes. This way I have the confidence that I can change 90% of the water in any of my tanks with no ill effects, or even move all my fish into a brand new tank (but of course that would need cycling!). These water changes also mean that any other stuff that finds its way in is diluted.

This is one of the best paragraphs I have read in all my time on this forum.

We tend to want to oversimplify everything, and make it black and white. As aquarists though, we're dealing with evolution, and asking questions is more important than receiving answers. We have to look at fish as species, and not as 'fish'. What a goldfish can tolerate in terms of nitrate and what a Central African Cichlid can handle are night and day apart. A truth for a fish adapted to pristine water you or I could scoop up and drink will look like a myth with a fish that lives and breeds in sewage outflow.

The advice you'll see aims at general conditions. It rarely takes into account diversity and different needs.