文摘
The Serrasalmidae is a speciose family of Neotropical freshwater fishes with diverse interspecies dietary preferences, from the herbivorous or frugivorous pacus to the omnivorous or carnivorous piranhas. The Serrasalmidae is an ideal comparative model to explore the biochemical correlates of dietary preference. For example, debate exists about whether variation in dietary preference among fishes influences the capacities for de novo glucose synthesis (gluconeogenesis) or glucose use as metabolic fuel (glycolysis). We predicted that carnivory in piranhas would be associated with an enhanced gluconeogenic capacity compared with the herbivorous pacus, because carnivores consume less carbohydrate. As a corollary, we expected similar glycolytic capacities at a major site of glucose use (heart) in fishes with different diets. We measured activities of key enzymes of gluconeogenesis and the opposing reactions of glycolysis in liver (the primary gluconeogenic site) and heart of five serrasalmid species showing an interspecies dietary gradient from herbivory to omnivory to carnivory. The interspecific variation in enzyme activities was, in general, unrelated to dietary preference. Glycolytic capacity in heart was lower in herbivores but this may be related to non-diet factors. Among serrasalmid fishes, the enzymatic capacities of glucose metabolism are not overtly influenced by interspecific divergence of dietary preference.