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Question: Axolotls & Gravel - Gastrolith/buoyancy aid or not?

AxolotlChris

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This question has probably been discussed to no end.. but I'm interested in our members current thoughts on the subject.

I had been looking around the web at information on Axolotls biotope in relation to substrate, when I came across this document: http://www.dinosaurhunter.org/files/app-2007-wings-gastrolith_function_classification.pdf.

It also turns out that Wikipedia uses this document as reference to their section on 'Captive Care' where they state 'There are persistent statements in pet care literature that axolotls cannot be kept on gravel because gravel causes fatal digestive impaction. There is no evidence to support this myth and counter evidence that normal healthy axolotls regularly ingest gravel and pass it without any negative consequences. The axolotl, like many amphibians, may be deliberately ingesting gravel to act as a gastrolith providing buoyancy control and aiding digestion, preventing impaction, rather than causing it. Axolotls deprived of appropriately sized gravel will ingest anything else they can find while attempting to satisfy their instinctive need for gastroliths and this behaviour, combined with lack of appropriate gastroliths, may be a cause, among others, of fatal impaction'

Some of the information in the above linked document show its plausible that gravel is used in trituration of food, also information within this text seems to suggest substrate is used in buoyancy control: An Error Occurred Setting Your User Cookie

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Any thoughts ??
 

xxianxx

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I think who ever wrote the article has a pea for a brain. The two main problems i would have are the statements that no evidence exists to prove gravel causes impaction and lack of gravel in the gut can cause impaction. There is ample evidence of the first claim non for the second. Havent time to read the source of this info yet but will do so , there may be an interesting study which is being misused or i may find some more pea brained **** , eithers good for me lol
 

AxolotlChris

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Just found a thread from back in May that covers this subject to an extent: http://www.caudata.org/forum/f46-beginner-newt-salamander-axolotl-help-topics/f48-axolotls-ambystoma-mexicanum/f57-axolotl-general-discussion/102514-gravel-substrate.html

One user in that thread actually posted the links to what I have linked above, but no one discussed the information within them.

The document 'A review of gastrolith function with implications
for fossil vertebrates and a revised classification'
is quite interesting, looking at all the theories of gastrolith function, even those which are not generally accepted by the scientific community.

One section from the 'Summary' of this document states: 'It is clear that not all gastroliths have a physiological function. Accidental intake is relatively common in species with particular feeding habits (e.g., carnivorous taxa or ant−eaters). A low percentage of gastrolith−bearing individuals within a taxon indicates that gastroliths were accidentally ingested or fulfil a function that is not critical for survival (e.g.,Gionfriddo and Best 1999; Cheng et al. 2006).'

Seems to me that the gastrolith theory doesn't hold enough evidence to prove Axolotls use gravel for the reasons Wikipedia state, and that the article has used the reference of the study to benefit their own biased conclusion.

Can the entry on Wikipedia be changed? Surely its biased and with no true evidence?
 

auntiejude

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In order to discuss this subject you have to consider the different types of gravel available in the aquarium trade. Most commercially available gravel is design for fish tanks, and to provide high surface area for the growth of beneficial bacteria. It is rough and fairly porous, and typically 5-12mm in size. This makes it unsuitable for axolotls as they would struggle to pass large jagged pieces of stone if ingested.

Smaller smooth pieces are suitable, for example the Axogravel available in parts of Europe which are around 3mm.

As for the gastrolith theory, it may well have been of benefit in the wild lakes for axies to ingest small stones for this purpose when they were regularly feeding on insects, snails or crustaceans with hard shells and exoskeletons. However, in captivity, gravel is not necessary as a gastrolith as we feed them soft food - worms, insect larvae, pellets etc.

And since other substrates such as sand can provide adequate surface area for bacteria, and low-risk stones such as river rocks or slate pieces are available, there is no point taking the risk with gravel.
 

AxolotlChris

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That pretty much sums it up. Its pretty logical that sharp jagged gravel will cause internal issues, take the tahitian moon sand, its clearly jagged and sharp: http://www.caudata.org/forum/f46-beginner-newt-salamander-axolotl-help-topics/f48-axolotls-ambystoma-mexicanum/f59-axolotl-tank-set-ups-filters-substrate/104451-suitable-gravel-axolotl.html

So it seems logical that smooth rounded 3mm gravel would be easily passed in the event that gravel was eaten. But whether its worth any risk is down to the owner.

From what I can tell, lake Xochimilco's bed is a mud/plant based. So sand and gravel is really not a natural substrate.

Seems more likely that Axolotl eat gravel by accident, I can't ever see an Axolotl picking out stones from a lake bed as a gastrolith. Its more likely Axolotl mistake gravel as food.
 
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