Wood eating loricariids 1

[lfinley58]

This and the following post add some quite interesting information to the wood eating loricariids topic. Note: Some of the special features in the abstract are absent...sorry about that.

Lee

Digestive enzyme activities and gastrointestinal fermentation
in wood-eating catfishes
Donovan P. German · Rosalie A. Bittong.
J. Comp. Physiol B, July 1, 2009.

Abstract To determine what capabilities wood-eating and
detritivorous catfishes have for the digestion of refractory
polysaccharides with the aid of an endosymbiotic microbial
community, the pH, redox potentials, concentrations of
short-chain fatty acids (SCFAs), and the activity levels of 14
digestive enzymes were measured along the gastrointestinal
(GI) tracts of three wood-eating taxa (Panaque cf. nigrolineatus
“Marañon”, Panaque nocturnus, and Hypostomus pyrineusi)
and one detritivorous species (Pterygoplichthys
disjunctivus) from the family Loricariidae. Negative redox
potentials (-600 mV) were observed in the intestinal fluids
of the fish, suggesting that fermentative digestion was possible.
However, SCFA concentrations were low (<3 mM in
any intestinal region), indicating that little GI fermentation
occurs in the fishes’ GI tracts. Cellulase and xylanase activities
were low (<0.03 U g¡1), and generally decreased distally
in the intestine, whereas amylolytic and laminarinase activities
were five and two orders of magnitude greater, respectively,
than cellulase and xylanase activities, suggesting that
the fish more readily digest soluble polysaccharides. Furthermore,
the Michaelis–Menten constants (Km) of the fishes’
-glucosidase and N-acetyl--D-glucosaminidase enzymes
were significantly lower than the Km values of microbial
enzymes ingested with their food, further suggesting that the
fish efficiently digest soluble components of their detrital diet
rather than refractory polysaccharides. Coupled with rapid
gut transit and poor cellulose digestibility, the wood-eating
catWshes appear to be detritivores reliant on endogenous
digestive mechanisms, as are other loricariid catWshes. This
stands in contrast to truly “xylivorous” taxa (e.g., beavers,
termites), which are reliant on an endosymbiotic community
of microorganisms to digest refractory polysaccharides.

http://www.springerlink.com/content/n00 ... lltext.pdf