Oxygen consumption in weakly electric Neotropical fishes

Abstract

Weakly electric gymnotiform fishes with wave-type electric organ discharge (EOD) are less hypoxia-tolerant and are less likely to be found in hypoxic habitats than weakly electric gymnotiforms with pulse-type EOD, suggesting that differences in metabolism resulting from EOD type affects habitat choice. Although gymnotiform fishes are common in most Neotropical freshwaters and represent the dominant vertebrates in some habitats, the metabolic rates of these unique fishes have never been determined. In this study, O(2) consumption rates during EOD generation are reported for 34 gymnotiforms representing 23 species, all five families and 17 (59%) of the 28 genera. Over the size range sampled (0.4 g to 125 g), O(2) consumption of gymnotiform fishes was dependent on body mass, as expected, fitting a power function with a scaling exponent of 0.74, but the O(2) consumption rate was generally about 50% of that expected by extrapolation of temperate teleost metabolic rates to a similar ambient temperature (26 degrees C). O(2) consumption rate was not dependent on EOD type, but maintenance of "scan swimming" (continuous forwards and backwards swimming), which is characteristic only of gymnotiforms with wave-type EODs, increased O(2) consumption 2.83+/-0.49-fold (mean+/-SD). This suggests that the increased metabolic cost of scan swimming could restrict gymnotiforms with wave-type EODs from hypoxic habitats.

The energetics of electric organ discharge generation in gymnotiform weakly electric fish

“…It is important to note that this is relative to routine levels, which in gymnotiforms are about 50% lower than in temperate teleosts (Julian et al, 2003). Julian and colleagues also showed that much of the variation in metabolic cost could be explained by scan swimming (exhibited only by wave-type fish) rather than EOD type (Julian et al, 2003). Such moderate swimming (about 1-1.5 body lengthss -1 ) results in a 3-to 5-fold increase in M O2 from routine levels (Julian et al, 2003;Moorhead 2010).…”

“…This suggests that the EOD comes at a relatively high cost. It is important to note that this is relative to routine levels, which in gymnotiforms are about 50% lower than in temperate teleosts (Julian et al, 2003). Julian and colleagues also showed that much of the variation in metabolic cost could be explained by scan swimming (exhibited only by wave-type fish) rather than EOD type (Julian et al, 2003).…”

“…μmolg (assuming the appropriate fish mass) and then multiply this by 5 ATPO 2 -1 to get the rate of ATP use. Oxygen consumption varies widely depending on species and body mass (Julian et al, 2003) (see Table1), but here we consider the two species for which we have the most data, the wave-type Eigenmannia cf. virescens (Moorhead, 2010;Reardon et al, 2011) and the pulse-type Brachyhypopomus gauderio (Salazar and Stoddard, 2008 ) for a 14g fish; assuming a 25Hz pulse frequency, the cost would be 1.7×10…”

“…That said, other studies of these fish have not found a strong association between energy consumption and electric discharge properties (e.g. Julian et al, 2003). To better understand these apparent contradictions, as well as the role energetics may have played in the evolution of bioelectrogenesis and electrosensory processing in weakly electric fish, we present a bottom-up analysis of the associated energetic costs, followed by a comparative analysis of electric signal features.…”

A taxonomic revision of the Neotropical electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes: Hypopomidae), with descriptions of 15 new species

“…A culteriform (knife-shaped) body plan facilitates maximum dipole separation of the fish as a dipole source (and therefore maximizes field strength per unit body mass, Stoddard et al, 1999), and optimizes use of the body surface as a relatively rigid electroreceptive array. Locomotion by undulation of the elongated anal-fin permits backwards-forwards electroreceptive rostral probing ('scan swimming' sensu Julian et al, 2003) Lannoo & Lannoo, 1993;Lissmann, 1961;Nanjappa et al, 2000;Stoddard et al, 1999) (in addition to anal-fin locomotion, Brachyhypopomus also swim in rapid bursts by anguilliform movement of the body when startled, Ellis, 1913). Body rigidity is augmented by ossified intermuscular bones (Schlesinger, 1910).…”