Digestive enzyme activities and gastrointestinal fermentation in wood-eating catfishes

Abstract

To determine what capabilities wood-eating and detritivorous catWshes 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 Xuids of the Wsh, 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 Wshes' 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 Wve and two orders of magnitude greater, respectively, than cellulase and xylanase activities, suggesting that the Wsh more readily digest soluble polysaccharides. Furthermore, the Michaelis-Menten constants (K m ) of the Wshes' -glucosidase and N-acetyl--D-glucosaminidase enzymes were signiWcantly lower than the K m values of microbial enzymes ingested with their food, further suggesting that the Wsh eYciently 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.

Stable carbon and nitrogen incorporation in blood and fin tissue of the catfish Pterygoplichthys disjunctivus (Siluriformes, Loricariidae)

“…Second, isotopic incorporation appears to be primarily driven by catabolic tissue turnover in slowly growing adult fishes. And third, P. disjunctivus cannot assimilate carbon from the fibrous portions of detritus, and, consistent with its digestive physiology (German and Bittong 2009;German et al 2010), probably does not use recalcitrant polymers (e. g., cellulose) as a resource in the wild. Plasma solutes incorporated 13 C and 15 N more quickly than RBCs in P. disjunctivus.…”

“…German (2009b) showed that neither P. disjunctivus nor Panaque nigrolineatus (a true wood-eating catfish) could assimilate significant amounts of organic matter (12.76% and 11.37%, respectively) or lignocellulose (32.08% and 23.69%, respectively) from a strictly wood diet in the laboratory, and both species lost weight when consuming solely wood. This inability to digest cellulose in their GI tracts comes from rapid gut transit (<4 h; German 2009b) and low cellulase activities (German and Bittong 2009). However, the fish are efficient at digesting soluble components of detritus (e.g., α-glucans, laminarin, β-glucosides, β-mannosides; German and Bittong 2009;German et al 2010).…”

“…This inability to digest cellulose in their GI tracts comes from rapid gut transit (<4 h; German 2009b) and low cellulase activities (German and Bittong 2009). However, the fish are efficient at digesting soluble components of detritus (e.g., α-glucans, laminarin, β-glucosides, β-mannosides; German and Bittong 2009;German et al 2010). This is further supported by the C incorporation in P. disjunctivus on the artificial wood-detritus, and the similarity between the predicted δ 13 C signature of the artificial wood-detritus diet and the δ 13 C of the fish's tissues.…”

Digestive Enzymes in Larvae and Juveniles of Farmed Sharpsnout Seabream (Diplodus puntazzo) (Cetti, 1777)

“…Others authors [96] examined digestive enzyme activities, luminal carbohydrate profiles, and gastrointestinal fermentation in xylivorous and detritivorous loricariids catfishes to determine if these animals were capable of digesting a diet rich in refractory polysaccharides, and whether they were reliant on an endosymbiotic community to do so. The results showed that wood-eating catfishes are not reliant upon endosymbionts to digest refractory polysaccharides [96].…”

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

“…Studies on other herbivorous fish have revealed the presence of a diverse hindgut microflora responsible for producing short chain fatty acids via fermentation, which are absorbed and metabolized by the fish [12,26]. However, comprehensive studies examining digestive enzyme activity levels, concentration of fermentative end-products, and gut transit time indicate that Panaque are detritivores and do not obtain energy directly from the digestion of wood [25,27], although the fish do swallow microbes associated with the wood and by-products generated by microbial wood degradation within the GI tract [28]. Thus, the Panaque GI tract provides an interesting environment-a vertebrate host GI tract enriched in cellulose and other recalcitrant wood compounds-offering an attractive system for discovery of new microbial species and novel enzymes.…”