Hmmm...that was my first thought as well. Perhaps I'm overstating, but I feel that sort of journalism is a bit irresponsible especially considering the lack of scientific evidence to support it.
The problem with this statement is that it isn't true.
As I mentioned on another thread it was my original email to Nathan that spurred his blog post.
so, a little background.
I have Danios. I'm also interested in the science part of fishkeeping. which essentially follows from my low tech approach.. a kind of walstad style. (ish)
While reading about Danios I soon realised 2 things. They're of extremely high importance to 'Science' and because of this have been investigated thoroughly and this isn't new, its been going on for years. This makes the species fairly unique within the hobby as the only fish we're likely to keep that has had any genuine research done upon them. (some of the findings are really fascinating and eye popping in their implications - but I digress.)
I came across a website devoted to the maintenance of these fish in Laboratories. It should be fairly obvious that keeping the species in perfect health is the only way to get good results. If you're doing research into a gene or genes related to (for example) Ageing. Then a fish or group of fish that die early due to some other factor or have a chronic illness - can upset your findings. It can destroy months or even years of work at a stroke. any paper that was going to result from the research will be worthless.
This site I mentioned is operated by the University of Oregon. They have a section devoted to disease. some i had heard of. some not. This entry stood out:
Nephrocalcinosis
This condition occurs in many species of fish held in captivity, and we occasionally observe it in our diagnostic cases. Nephrocalcinosis is the accumulation of calcium deposits in kidney tubules and collecting ducts. Causes of nephrocalcinosis include high CO2 (e.g., > 12 mg/L) in water or excessive levels of calcium and magnesium in the diet. The use of calcium carbonate (rather than sodium bicarbonate) to buffer water in recirculating systems has been associated with the condition (
Chen et al. 2001). Only when the lesions are extensive is the condition associated with overt clinical disease. In other words, we see many fish with the condition (diagnosed by histology) in which it was probably not a significant cause of the disease.
Clinical Signs and Gross Pathology. We have not observed macroscopic changes due to nephrocalcinosis in zebrafish. However, with larger fish, kidneys with severe nephrocalcinosis may exhibit distinct, white, opaque deposits in the kidney. The ureters may be filled with a chalk-like material, and vermiform deposits may occur in collecting ducts and tubules.
Microscopy. Histological sections reveal basophilic, crystalline deposits (uroliths), in renal tubules and collecting ducts. The deposits often cause severe dilation of the affected structures.
Click for high resolution image
Histological section showing masses of basophilic crystalloid material (arrows) in kidney tubules and collecting ducts
Diagnosis. Observation of calcium (basophilic) accumulations in the kidney by histology is generally sufficient for confirmatory diagnosis.
Control and Treatment. With zebrafish, high CO2 associated with crowding or the use of calcium carbonate (e.g., crushed coral) are two factors that have the potential to cause nephrocalcinosis.
Chen et al. (2001) recommended buffering with sodium bicarbonate. In addition, proper CO2 concentrations should be maintained by proper water exchange and avoiding crowded conditions. Proper atmospheric CO2 levels should be maintained by appropriate ventilation.
end.
Obviously i didn't leave it at that.. it didn't take long to find a multitude of papers that addressed this problem.. nearly all in the fish farm industry. It was first recognised as a problem in the early 1970s and since then has been largely forgotten about. With the method of prevention being so simple.. its really no longer an issue. Its reappeared in more recent times due to side effects of other problems in as an example the Baltic sea fishery. elevated CO2 due to environmental factors. pollution etc.
To say there is a lack of evidence to support it is much like suggesting Rickets isn't a problem. we know the cause, we know how to prevent it. Its now extremely rare in western society. so why do any more research? thats probably a terrible analogy. ho hum.
The problem we face is that there has been no research. the levels of CO2 in 'High tech' aquaria do not, as far as I can tell exist in nature. All the people with a financial interest avoid it like the plague. Obviously the quote above means its still seen in laboratory fish. And that resource can then be called upon by any research team that find it in autopsied fish. "ah.. calcium deposits. we need to look at the co2 levels in our fry and holding tanks."
I thought this was interesting stuff. but I didn't know what to do with it. so, before unleashing hell by starting a thread i gave a moderator on the PFK forum the heads-up. He told me to get in touch with Nathan Hill.. who, it appeared found the entire thing fascinating and wrote his piece.
its pretty obvious to me that this is likely an issue. but Im not daft, Ive seen fish in CO2 injected tanks and they 'appear' absolutely fine. But, after I came across this information i wondered if that was really the case. are they really as fine as they look. I can't honestly answer that. but i think it is at least worth considering.. and hopefully at some point. a definitive answer will be forthcoming.