Inside the guts of wood-eating catfishes: can they digest wood?

Abstract

To better understand the structure and function of the gastrointestinal (GI) tracts of wood-eating catWshes, 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 catWshes 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 proWles 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 proWles and gastrointestinal fermentation levels in the Wshes' GI tracts, suggesting that the wood-eating catWshes are not true xylivores such as beavers and termites, but rather, are detritivores like so many other Wshes from the family Loricariidae.

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

“…Loricariid catfishes are resilient animals, which lack scales, and endure handling stress with little side effects. For example, P. disjunctivus in this and previous investigations (German 2009b;German et al 2010) always consumed food following handling. This is probably why this fish species (and its close relatives) are popular in the aquarium trade and are successful invaders in novel habitats.…”

“…Twenty-two adult Pterygoplichthys disjunctivus were captured by hand while snorkeling from the Wekiva Springs complex in north central Florida (28º41′48.9″ N,81°23′27.84″ W) (German 2009b). We housed the fish in pairs because preliminary observations suggested that the fish were less stressed and commenced feeding immediately when in the presence of conspecifics.…”

“…Because previous observations suggested that P. disjunctivus did not gain weight on a wood-only diet in the laboratory (German 2009b), we included a group of fish that acted as negative controls. Six individuals (BM±SD; 307.52±134.40) were deprived of food for the duration of the wood-feeding experiment (155 days).…”

“…b cellulose and hemicellulose (collectively called holo-cellulose) isolated from wood following Gaudinski et al (2005); proportion determined on an organic matter basis, and mass presented represents 51.1% (German 2009b) of 80 g of bulk wood; not an additional ingredient c gifts from Hartz-Mountain Corp. and intended specifically for use in fish food d indigestible non-starch polysaccharide added as a binding agent to keep pellets bound in water was examined and the contributions of growth vs. catabolic tissue turnover determined. This is a necessary step in our understanding of isotopic dynamics in fish tissues, especially since many stable isotopic investigations of wild-caught fishes utilize adult animals that grow slowly or seasonally (Perga and Gerdeaux 2005).…”

“…This is a necessary step in our understanding of isotopic dynamics in fish tissues, especially since many stable isotopic investigations of wild-caught fishes utilize adult animals that grow slowly or seasonally (Perga and Gerdeaux 2005). In this study we examined tissue isotopic turnover in Pterygoplichthys disjunctivus (Weber 1991), a detritivorous (German 2009b) suckermouth armored catfish (family Loricariidae), congeners of which are now found throughout central and southern Florida (Nico 2005;Nico et al 2009), among other locations throughout the globe (Page and Robbins 2006;Mendoza et al 2007), where they have caused considerable disturbance and have become the dominant fish taxa in some habitats (Nico 2005;Mendoza et al 2007;Nico et al 2009). Two stable isotopic turnover experiments were conducted.…”