Can Plecos Digest Wood?

[Coryloach]

Some quotes from R.D.'s link for those lazy to read the entire article...

http://german.bio.uci.edu/images/PDF/German (2009) JCPb_gut_print.pdf


The data gathered in this study clearly support the null hypothesis that the “xylivorous” loricariid catfishes do not efficiently digest the fibrous components of wood in their GI tracts.

In conclusion, the wood-eating catfishes in the family Loricariidae appear to be detritivores more so than true xylivores. They display none of the anatomical adaptations other xylivorous animals possess for the harboring of endosymbionts, and their digestive tracts are similar in shape and size to closely related detritivorous fishes.

However, the wood-eating catfishes do take macroscopic detritus (i.e., woody debris) and reduce it to <1 mm in diameter, which likely has signiffcant consequences for carbon cycling in their environment.

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

.....suggesting that the wood-eating catfishes are not true xylivores such as beavers and termites, but rather, are detritivores like so many other Wshes from the family Loricariidae.

 

[RD.]

I liked this portion of the interview, hopefully it's available online for years to come. http://german.bio.uci.edu/PFK_response.html

"Fifth, the difference between the words “eat” and “digest” must be defined. “Eat” means to consume. That is it. The word “eat” does not imply that whatever was consumed can be digested and utilized in a nutritional manner by an animal.

The word “digest” implies that what was eaten can be broken down (i.e., digested) by hydrolytic enzymes in the GI tract of an animal and absorbed for use in a nutritional context. To use these two words in a real life example: Parrotfishes eat coral. There is no denying that the parrotfishes consume a considerable amount of coral (and by this I mean the hard, calcium carbonate reef); gut content analyses show that the fish eat coral. However, parrotfishes do not only eat coral, and they certainly do not digest coral in their guts. There simply isn’t any nutritional value to carbonates. Many parrotfishes are actually detritivores, taking bites of reef to access the nutritional detritus that has collected in the interstitial spaces of the reef (Crossman et al. 2005).

Much in the same way, the wood-eating catfishes “eat” a considerable amount of wood (~70% of their intake). However, they poorly “digest” the bulk wood (the cellulose and lignin of the wood proper), but efficiently digest detritus and wood degradation products (e.g., disaccharides). I hope this analogy helps. Wood is the reef in the Amazon, providing critical habitat to so many fish species. Wood-eating catfishes, therefore, are the parrotfish of the Amazon, not the beavers of the fish world (as I commonly end my talks). I just want to make it clear that I never said that Panaque do not “eat” wood. They certainly do. The wood-eating catfishes just poorly “digest” wood itself. "

 

[Joshomaru]

Very appropriate comparison to the parrot fish. The wood is a by product of the the feeding habit, therefore, the panaque's gut has "learned" to deal with wood (or in the parrotfish's case, coral), to glean the nutrition associated with the wood (like the lettuce on a big mac).
Thanks for the cool read!

 

[RD.]

No prob, glad that some members here found it interesting.

 

[thefredpit]

all information about my obsession is good information

 

[RD.]

bumping for anyone that missed this …..

 

[LBDave]

Studies such as those by Fang Zhang and R. McDonald (ISME 2015) determined that
P. nigrolineatus GI tract provides a suitable environment for nitrogen fixation and in combination with its xylivorous (feeding on wood) ability.
Pleco owners - don't throw your driftwood away!

 

[RD.]

My posting here was not to suggest that anyone should not keep driftwood with their plecos, or throw it out? Only that aquarium driftwood should not be considered as a source of nutrients for their fish.

 

[kshkong97]

Thanks for the info!

 

[TwoTankAmin]

I realize this is an old thread, but the science on this issue did not stop with the article referenced here. There is subsequent research, more in depth. This research indicates some of the failures of the German study. I will provide all the links needed to read this paper after providing two quotes from it. Apparently the xylivores do not digest wood directly to extract nutrition from it, rather they have gut bacteria which does the breaking down and then the fish get the nutrition via the bacteria.

3. Results and Discussion

Wood-eating Panaque spp. provide an attractive system to examine microbial communities
associated with a high cellulose-enriched vertebrate GI tract. Fluorescence microscopy of non-aqueous
Carnoy’s-fixed tissue stained with DAPI (Figure 1) revealed a distinct mucus layer adhering to the
intestinal wall that was extensively colonized by microbial bacillus and coccoidal cells. This mucus
layer was most prevalent in the foregut, but also extended into the mid- and hindgut regions. This
structure was often seen attached to the epithelial lining, but occasionally extended into the lumen
contacting the digesta, which is likely a result of the mucus pulling away from the intestinal wall
during tissue dehydration. Attempts to visualize a mucus-associated community in 4%
paraformaldehyde-fixed tissues were unsuccessful, which may be explained by the inability of
formaldehyde-based fixatives to preserve mucus [49]. Non-fixed mucus is easily destroyed by the
mechanical forces of the wash steps. These findings may explain the discrepancy between results
reported here and those of German (2009) who examined the GI tract of Panaque sp. using scanning
electron microscopy of 4% paraformaldehyde-fixed tissues and reported the absence of any bacterial
cell conglomerations. Although qualitative, the highest densities of microorganisms could be observed
in the mucus membrane; however, bacteria could also be detected attached to wood particles.

4. Conclusions

Panaque spp. possess a number of morphological adaptations that could support the ability to
obtain dietary supplements from a resident microbial community located in the mucus layer along the
GI tract surface. These adaptions include spoon-like teeth for eating and scraping wood [22] and a long
GI tract providing a high surface area for microbial colonization. Our results suggest that the
P. nigrolineatus GI tract contains a microbial community that has the capacity to degrade cellulose and
are likely to be involved in the breakdown of cellulolytic substrates. The fish may obtain energy by
digesting this microbial population, a strategy that is consistent with recent studies using isotope
tracking, which found that wood-eating loricariids are assimilating microbially-derived carbon [28].
Our study provides the first images and culture based studies providing compelling evidence for a
specialized microbial community involved in cellulose digestion within the P. nigrolineatus GI
tract and is the basis for ongoing studies focusing upon the molecular analysis of microbial
cellulose-degrading population present in this interesting wood-consuming vertebrate.

Examination of a Culturable Microbial Population from the Gastrointestinal Tract of the Wood-Eating Loricariid Catfish Panaque nigrolineatus

Joy E. M. Watts 1,, Ryan McDonald 2, Rachelle Daniel 3 and Harold J. Schreier 2

1 Department of Biological Sciences, University of Portsmouth, Portsmouth PO1 2DY, UK
2 Departments of Marine Biotechnology and Biological Sciences, University of Maryland Baltimore County, Baltimore, MD 21250, USA
3 Department of Biological Sciences, Towson University, Towson, MD 21252, USA

Received: 22 May 2013 / Revised: 2 August 2013 / Accepted: 13 August 2013 / Published: 19 August 2013
From https://www.mdpi.com/1424-2818/5/3/641