Panaque - Respiration in wood-eating catfishes

[Walter]

J. A. Nelson:
Respiration in wood-eating catfishes

Abstract:
The use of woody plant material as a dietary item is rare among vertebrates and unknown in fishes. Previous work has shown that loricariid catfishes of the genus <CITE>Panaque</CITE> have teeth which appear to be specialized for gouging, and that individual <CITE>Panaque</CITE> can be captured with gastrointestinal tracts filled with wood shavings. The cental question I address here is whether these animals are taking advantage of poor-quality carbon merely by lowering their metabolic rate and reducing metabolic demand (hypometabolism). If they are, <CITE>Panaque</CITE> are less likely to have any specialized adaptations for digesting wood and their digestive physiology would be less interesting to study . I have taken advantage of the burrow-dwelling nature of this genus to obtain reproducible measurements of their metabolic rate. Artificial cave-respirometers were built into the sides of aquaria; fish would enter these artificial caves of their own volition and measurements easily taken by sealing the entrance. Thus, it was possible to obtain oxygen consumption data over long periods (Clark-type pulsed DO probe) without handling or disturbing the animal. To date, I have obtained measurements of resting routine metabolic rate and specific dynamic action (SDA) for two species of <CITE>Panaque</CITE> being held on a variety of diets. Although size-adjusted metabolic rates for <CITE>Panaque</CITE> are low for fishes of this size, they are within the range expected for catfishes. Metabolic rate did not vary with diet quality, suggesting that, since individual <CITE>Panaque </CITE>are capable of growth on a "wood-only" diet, they should possess interesting adaptations for exploiting low-quality carbon sources unavailable to other fishes. Therefore, research into the natural history and digestive physiology of this interesting genus should commence before any of these fishes are lost to the habitat degradation occurring in their native range.

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Panaque Research