Wood eating loricariids 2

[lfinley58]

This is a copy of the original thread here:
http://www.planetcatfish.com/forum/view ... 14&t=27505
As the Taxonomy and Science forum is more of an announcement forum, I've moved the posts here.

--
Mats

Enjoy!

Lee

Inside the guts of wood-eating catfishes: can they digest wood? by Donovan P. German. J. Comp. Physiol. B, June 27, 2009.


Abstract To better understand the structure and function
of the gastrointestinal (GI) tracts of wood-eating catfishes,
the gross morphology, length, and microvilli surface area
(MVSA) of the intestines of wild-caught Panaque nocturnus,
P. cf. nigrolineatus “Marañon”, and Hypostomus
pyrineusi were measured, and contrasted against these same
metrics of a closely related detritivore, Pterygoplichthys
disjunctivus. All four species had anatomically unspecialized
intestines with no kinks, valves, or ceca of any kind.
The wood-eating catfishes had body size-corrected intestinal
lengths that were 35% shorter than the detritivore. The
MVSA of all four species decreased distally in the intestine,
indicating that nutrient absorption preferentially takes
place in the proximal and mid-intestine, consistent with
digestive enzyme activity and luminal carbohydrate profiles
for these same species. Wild-caught Pt. disjunctivus, and
P. nigrolineatus obtained via the aquarium trade, poorly
digested wood cellulose (<33% digestibility) in laboratory
feeding trials, lost weight when consuming wood, and
passed stained wood through their digestive tracts in less
than 4 h. Furthermore, no selective retention of small particles
was observed in either species in any region of the gut.
Collectively, these results corroborate digestive enzyme
activity profiles and gastrointestinal fermentation levels in
the fishes’ GI tracts, suggesting that the wood-eating
catfishes are not true xylivores such as beavers and termites,
but rather, are detritivores like so many other fishes
from the family Loricariidae.

http://www.springerlink.com/content/301 ... lltext.pdf

[Suckermouth]

Nice, I didn't know there were other people looking at this system. I was going off of Nathan's word when he told me about wood-eater digestive tracts, so it's good that I can cite something now.

I wonder if we could merge the topics? I'm going to comment on both of them here since both papers are about the same system... They're probably both chapters from German's dissertation, not that I've seen it.

I'll have to read this later, I just looked at the abstract so far.

[MatsP]

I don't really want to merge the topics. I will split off the other topic, and move the whole thing into Loricariidae section, and then put links to these two subjects (in a bit, as I have other things to do right now, just checking in quickly). I believe this forum isn't really for DISCUSSING the findings in the literature, but rather to announce new scientific work.

--
Mats

[Jools]

I don't really want to merge the topics. I will split off the other topic, and move the whole thing into Loricariidae section, and then put links to these two subjects (in a bit, as I have other things to do right now, just checking in quickly). I believe this forum isn't really for DISCUSSING the findings in the literature, but rather to announce new scientific work.

Agreed.

Jools

[Suckermouth]

What is a forum for if not to discuss? Forgive me for assuming that a topic about a scientific paper is not the correct place to discuss the findings and its implications. I can see how my prior discussion may have been of tangential relationship to warrant a split, though. So if I want to raise points based on a newly published paper I should post a topic in another forum and link back here? Not to start an argument, but that seems unnecessarily indirect as well as redundant when a topic is already available. But since you guys don't think this is the place to discuss these papers, I guess I'll shut up then.

[MatsP]

The purpose of THIS forum is to announce news in the scientific world. Discussions on the content of these papers belong in the respective forum for the fish involved (e.g Loricariidae forum) - unless it's some sort of amendment/clarification(-request)/criticism directly of the paper itself.

I'm aware that understanding of the forum culture is not innate knowledge, so I'm happy to help correct things when they go wrong, as I'm sure most other moderators are.

--
Mats

[Jon]

While I realize gut die offs during transit is often considered a myth, I'd be interested in seeing some piece of work that contrasted freshly caught panaque microbial activity with that of 1) their surroundings and 2) their aquarium reared counterparts.

Unlike other textbook xylivores, panaque have the unique distinction of living in water, which allows free access of microbes to moisture. Therefore, perhaps, instead of requiring, and thus, burdening themselves with the microbial load and long digestion times of other wood eating organisms, panaque can simply sequester naturally decomposing wood, and harbor the microbes for extended periods within their GI cavities, which have already been shown to foster significant glycosidic lytic potential. Thus, their guts may aid in microbial digestion, but do not culture it.

Therefore, possibly because of incompatibility with or total lack of these relevant organisms in the home aquarium system, panaque need dietary supplementation, and hence, lose weight when fed on wood exclusively in these controlled situations.

[Bas Pels]

As I get the impression wood eating Loricarids preferr the soft, semi rotten partds of the trunk, I think you could very well be right Jon.

Why trouble oneself with complicated digestive organs, if pre-digested wood is available?

[Suckermouth]

Therefore, possibly because of incompatibility with or total lack of these relevant organisms in the home aquarium system, panaque need dietary supplementation, and hence, lose weight when fed on wood exclusively in these controlled situations.

I can believe that if there is a great importance for wood digestion by micro-organisms that it is simply something we do not replicate in the aquarium, at least not to an extent natural to these fish. Considering these fish are best at absorbing polysaccharides after being released from wood, I was trying to think of what kinds of foods we could use that have a lot of these. Unfortunately I haven't read the paper yet, but I'll have to see if German comments on what types of polysaccharides he thinks they digest best and see if there are any common foods that have those...

Large Panaque species in captivity are notorious for growing slowly, and bridging the gap in our knowledge of Panaque nutrition and digestion may allow for faster growth. Unfortunately there's not a great way to tell if Panaque grow equally slowly in nature; at least, not without counting otolith rings.

PS: Sorry Mats, I can't resist discussing! Split this off if you deem it appropriate, but I thought it would be confusing to try to respond to a reply here in another topic in another forum, instead of keeping it all together.

[Jon]

Of course, even if the secrets of panaque digestion are elucidated, there's still the matter of getting them to eat ;).