candiru revisited...fact or fiction

Dave Rinaldo · Post by **Dave Rinaldo** » 26 Apr 2005, 13:47

I was discussing this with a member of our fish club. I told him I believed it to be a myth and he thought it to be true. He reminded me about this story.
This is from an earlier thread:

medaka wrote:i watched a t.v. programme on this fact/fiction
the programme claimed that the person who claimed to have been "attacked" in this way was none-other than the doctors
brother in law..and they were alledgedly making money selling their two stories, but not letting on that they were related.
i believe prior to this story there were only myths
and there were no factual evidence to back the stories up

Where does one take a stance on this...possible but unlikely to happen?

worton[pl] · Post by **worton[pl]** » 26 Apr 2005, 15:12

hmm I'm not sure about a chemistry of human urine, but I think that fish have to excrete a lot of the same substance through gills as humans through ... you know what :) and thats why we still have few cases of mistake commited by fish.

MatsP · Post by **MatsP** » 26 Apr 2005, 15:19

worton[pl] wrote:hmm I'm not sure about a chemistry of human urine, but I think that fish have to excrete a lot of the same substance through gills as humans through ... you know what and thats why we still have few cases of mistake commited by fish.

Nope, humans excrete urea, which is a organic binding of ammonia, but fish excrete ammonia straight away. I asked about this earlier in Speak Easy, and Silurus kindly explained how it works. Ammonia excretion requires lots of water to dilute the ammonia to safe concentrations. Since humans (and mammals, reptiles and birds) are adapted to life on land, the need to conserve water is greater than the need to release the simplest form of compound, so we've developed to excrete urea, and fish remaing excreting ammonia.

So, unless the candiru have severely bad sense of smell for a fish, it shouldn't get confused. [I haven't got particularly good sense of smell, but I can certainly tell ammonia from just about ANYTHING else].

That in itself doesn't mean that this fish hasn't developed to also use urea to latch onto animals(mammals) that are in the water. Whether this is so or not, I don't know.

--
Mats

worton[pl] · Post by **worton[pl]** » 26 Apr 2005, 16:53

That make sense but I'm still confused a little bit :).
Ok so candiru cats have to smell pure ammonia since it's imho rather impossible that they are mammals parasites - so maybe fish excrete something else than only ammonia through gills?

And there is something else, as effect of concentration of two molecules of urea we get something (with very compliated formula) and NH3 - however I don't know if concentration process is possible in human body.

And humans got all system of organ that let them hmm pissing - fish excrete most part of ammonia through gills, the same organ which they use for breathing. What Ph got water where candiru live?

Dave Rinaldo · Post by **Dave Rinaldo** » 26 Apr 2005, 17:40

I guess my question is if this info was ever confirmed/debunked

Here is the thread with my response on my clubs forum.

natefrog · Post by **natefrog** » 26 Apr 2005, 17:51

Not all fish excrete just ammonia, (Ammonotelism), and it is not just through the gills that fish remove metabolic by-products. True urea is a mammal/amphibian excretion; however, fish may also excrete nitrogenous waste in the form of urea, (Ureotelism). In the life cycle of many organisms they may excrete waste in two or more forms as well. I don't know whether fish remove any urea through vascularized tissue, but I would suspect not, due to its reduced ability to easy pass across cell membranes, (think gills).
-just a few thoughts

pturley · Post by **pturley** » 28 Apr 2005, 21:54

If you read Stephen Spott's book Candiru (which I DON'T recommend BTW) you'll note, all of their experiments to determine if these fish were attracted to dilute urine or ammonia failed.

The assumption that these fish are attacted to ammonia from larger fishes' gills is likely just that. The fact it's quoted OVER and OVER again is nothing short of incredible. In the past, I likely quoted this theory too. But that's it. It was ("is" in some circles) a theory.

Remember this one.. "ass-u-me"

The book does provide a couple other theories on how the fish locate their prey.

Chrysichthys · Post by **Chrysichthys** » 01 May 2005, 13:03

Does anybody want a repeat of my candiru limerick? It's not in the best of taste.