| Brycon guatemalensis Regan, a Neotropical characid fish, consumes an entirely terrestrial diet, shifting from eating insects as juveniles to fruits and leaves as adults. I studied juvenile (42–78 mm standard length, LS) and adult (225–414 mm LS) size classes collected in the Rio Puerto Viejo at the La Selva Biological Station in Costa Rica to test the hypotheses that with ontogeny (1) relative gut length increases, (2) pyloric caeca arrangement remains unchanged, and (3) pepsin, trypsin, and lipase activities decrease, while α-amylase activity increases. The hypotheses were largely supported in that adult fish had longer guts, unchanged pyloric caeca arrangement, and, at both the environmental and standard temperatures for the enzyme assays, lower pepsin and trypsin activities but higher α-amylase and lipase activities than the juveniles. These results support the view that B. guatemalensis is specialized morphologically and biochemically to function first as a carnivore and then as an herbivore during its life history. |
