Aquaponics 101-Part One: The Process

[keith_r]

yes, at low levels it is non toxic, but at elevated levels and prolonged exposer.. there is plenty to show it will cause damage to fish... even tilapia, and that is something every budding ap enthusiast should know

first glance at data never reveals all details..

[urbanfarmer]

Toxicity is toxicity and studies relating to concentrations tell us what the effects are at those concentrations. When it says it's not toxic, it means it's not toxic. What first glance at data are you talking about? Your source is not raw data, your source is interpreted from raw data; therefore, it is information. Information you should be disseminating not arguing against.

P.S. The 1 quotation from a scientific source you have referenced does not dispute anything I have said. In fact, it supports it. I implore you to PLEASE PLEASE search for more information if you recall that you saw something about nitrate toxicity in fish. If nothing more, it will help you learn.

P.P.S. I do get heated about these things when I am 99.999% confident about things. That doesn't mean I'm always right, but in this case I feel this is very remedial (like you said) except you have it wrong. If somehow the vast amount of scientific literature I have reviewed is all wrong, then by all means please make your case. I just don't see how a fact commonly accepted in the scientific community, which is not under debate or is controversial, is something you wish to argue against... anyway... let me know what you think bud...

[keith_r]

so, i just want to get this straight.. you say nitrate is non-toxic to fish?

[urbanfarmer]

so, i just want to get this straight.. you say nitrate is non-toxic to fish?

I have stated it is non-toxic to Tilapia and likely non-toxic or a very weak toxin to most freshwater fish species that are commonly farmed and cultured in RAS systems for food. Yes, in the context of what I have said in this thread.

[keith_r]

ok then... here's a "real" study.. i'm not sure what is in your "folklore" category
http://www.atlantech.ca/public/articles ... uality.PDF

now.. levels must get staggeringly high to be toxic, and ras cultures have shown that tilapia will survive in 1000ppm, but bluegill will have trouble at 500ppm (i read the 500ppm part in an osu paper - ohio state univ... can't find it now.. ) the 1000ppm is something i heard from an aquaculturist so take it with a grain of salt..

[keith_r]

the only other thing i really have to say on this is that if my nitrate readings were that high, i would think there was a problem with my system, being underfiltered, overstocked, overfed... all of which can cause a crash..

[urbanfarmer]

I am reading, one sec please...

[rfeiller]

Sorry if I did not intend to type fish, but plants remove nutrients what minerals are extracted by fish I am not certain to what degree. I am typing blindly on

my phone and didn't see the mistyped word.

[urbanfarmer]

REVIEW OF: http://www.atlantech.ca/public/articles ... uality.PDF

Well, I call into question the quality of the research because as I read it certain things (based on my knowledge of water chemistry and fish biology) just screamed out at me. However, please note the researcher calls these same issues into question; therefore, I am not calling the quality of the researcher into question just the experiment itself. This happens A LOT in science. The experiment doesn't go the way you expected because, in the end, it is an experiment. Sometimes your control and changing of 1 variable ends up changing multiple variables. Sometimes you just make stupid mistakes and introduce error into your experiment (as is the case here). This can yield results that are not useful or not relevant to the original research question. I don't mean to painfully go over the fundamentals with you, but I have to preface my response with that...

A lot of the symptoms scream out to me nitrite poisoning, but in the discussion the researcher addresses this:

When nitrate levels were elevated due to addition of a nitrate salt or from nitrification, increased nitrite levels were observed. This increase in nitrite was most likely due to enhanced reduction of nitrate to nitrite caused by the elevated nitrate concentrations. (page 5)

In the end, I don't think toxicity was shown because the nitrate levels used did not kill the fish. The exception is the first experiment performed, but as the researcher stated it could have been caused by anything including ammonia or nitrite. If you notice when he examined a RAS with nitrate over 200 mg/L (ppm) the fish were not all dead and in fact in a commercial system. Clearly, something went wrong in his first experiment if there are commercial operations that don't have dead fish at these levels. To shed light on this I would like to explain there are bacteria that convert nitrate back to nitrite. In systems that have properly established cultures, the direction of this conversion is vastly in favor of nitrite to nitrate, but in his experiment it may not have been. This is further supported by his findings where the symptoms resemble nitrite poisoning. Coincidence or not, it should definitely raise some questions in your mind as it did for the researcher.

The changes observed in the nitrate treated fish most likely represent a pathological response as apposed to a generalized stress response. (page 6)

Again, the researcher has concluded that although nitrate MIGHT cause problems in RAS, it was not due to a nitrate toxicity. Instead, it was a secondary infection that did the fish in. As I stated earlier, I have seen scientific research discussing possible decline of immune system response in high concentrations of nitrate.

The water quality in this report was not mentioned, so it is not known if the nitrate concentrations were elevated. (page 6, end)

I was very disappointed when I read this. Maybe chloramine existed in the water and released large amounts of ammonia, chlorine, and nitrite into the water. Maybe the water contained other toxins that caused danger to the fish. I think you and I both know that pouring water out of your tap and then throwing some fish in is just a BAD idea. TSK TSK

Conclusion
The data presented here support the theory that prolonged exposure to elevated levels of nitrate may decrease the immune response, induce hematological and biochemical changes indicative of a pathologic response, and may increase mortality. If elevated nitrate levels are responsible for the pathologic changes seen in these fish, then management of recirculating systems must change to lower nitrate levels. The pathologic changes are sufficient to affect the normal physiology of the fish and will probably result in decreased growth and increased susceptibility to disease. These results however do not conclusively show that elevated nitrate levels are responsible for the pathology seen. Further studies demonstrating a dose response to nitrate levels should be conducted prior to making major management changes in a recirculating system.

Ultimately, I think this study is pretty bad. The experiment was poorly designed, and the researcher knows this as he describes all the flaws and leaves some out. Moreover, the researcher has no confidence in his findings nor can he make recommendations based on his findings. This is, in my opinion, not evidence to support nitrate toxicity in fish nor does it support the theory that nitrate causes a reduced immune response in fish (but perhaps does raise interest in the latter matter).

I think you will be hard pressed to find any evidence that supports nitrate toxicity in fish, which is why it is often presented as non-toxic in many textbooks. You have found one such textbook, and I am currently reading another titled "Aquaculture An Introductory Text (2nd edition)" and it was recently updated in 2009; so, I believe it to be up-to-date.

Please continue searching if you have the time and interest. I think you will find the process educational and enlightening. You will not regret it, and you will be better off for it. If you'd like, I can PM you a list of scholarly databases that are FREE to the public. I found they are about 10 years behind, probably why they are free, but that's not bad for us in aquaponics because we don't go into anything in depth and science has answered a lot of issues we face, at least to respect to aquaculture, hydroponics, and botany. I use other sources as well, but I have access to them as a student and it's not available to the general public, unfortunately.

[rfeiller]

Sorry if I did not intend to type fish, but plants remove nutrients what minerals are extracted by fish I am not certain to what degree. I am typing blindly on my phone and didn't see the mistyped word. ididn't intend to do anything to you.
In my thread about nitrate levels I was hoping to see a pattern of this level of nitrates is best for this type of veggie/ plant and which works best with which type of fish. It's a given tilapia are best economically raised in the south or at least a state where they are legal. The rest of us will use other types of fish. This information works best to prevent newbies from failure.