Fish which need driftwood.

[Dan F]

For example, porcupines assimilate about 70% of NDF from wood with similar biochemical composition to that offered to the fish in this study (Felicetti et al. 2000). P. nigrolineatus and Pt. disjunctivus did clearly assimilate some cellulose from wood [given the small increase in the lignin:cellulose ratio (Abril and Bucher 2002) in the feces compared to the wood], and potentially some lignin, although the latter is likely an artifact of the detergent Wber analysis system (Jung 1997), which was designed for grasses (Goering and Van Soest 1970), not wood; lignin is considered indigestible by vertebrate animals (Karasov and Martínez del Rio 2007).

Did you read this part?

I'm by no means arguing that you should be feeding your fish lizards and frogs. If people want to keep wood-eating plecos in tanks without wood, so be it.

However, to say that plecos "cannot digest wood" is completely erroneous.

While you may consider a 20-30% digestibility "extremely LOW" it really isn't all that low, especially considering that they assimilate that percentage very quickly - according to the article they pass the wood in a matter of four to six hours. I don't know how long it takes a porcupine to assimilate 70% of the wood, but I would expect it is a lot longer than four hours.

 

[RD.]

Yes Dan, I read that part ...... I read the entire paper & drew the same conclusions that the author of that paper did. Did you read those parts? As in the ones that I just posted? Can it be any clearer than that?

You're right, what I should have said in my initial comment in this discussion was;
Plecos do not require wood as part of their diet, and FOR THE MOST PART nor can they digest it.

Better?

If you go back to the original thread that I linked to, the one that I started in the pleco section a few months back, I clearly stated up front in my initial comment;

I have been suggesting to people for years that panaques etc. don't eat wood for it's nutrient value, or for digestibility, they eat it as a secondary action when scraping the biofilm that grows on the wood.

And yes, I realize that there was *some* digestion of the cellulose - whoopee! The total digestion stated in that paper is indeed low, EXTREMELY low, when one compares raw food stuffs typically being consumed by fish. Many raw ingredients fall in the 90+% digestibility category. If/when the digestibility of a food source is so incredibly low that a fish will actually lose weight while consuming it, as in the wood in this study, then yes, one can safely dismiss it's role as a source of nutrients.

It is for that exact reason why the author of that paper and those after him have basically dismissed the nutrient value of wood, when feeding plecos.


From the author of that paper via his interview with Matte Clarke ........

However, they poorly “digest” the bulk wood (the cellulose and lignin of the wood proper),

The wood-eating catfishes just poorly “digest” wood itself.

From his paper .........

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.

The data gathered in this study clearly support the null hypothesis that the &#8220;xylivorous&#8221; loricariid catfishes do not efficiently digest the fibrous components of wood in their GI tracts.

However, the one study published to date examining digestion in species of Panaque and Pterygoplichthys provided only inferential evidence of cellulose digestion (Nelson et al. 1999). The data gathered in the current study and that of German and Bittong (2009) systematically refute that wood-eating species in the genera Panaque or Hypostomus, or the detritivorous Pt. disjunctivus, have the capability to digest and subsist on wood.

If you find the above statements to be erroneous, Dan, feel free to take it up with Donovan German and those that supported his research & findings.



Over & out.