Abstract
The Axolotl, Ambystoma mexicanum, endemic to the freshwater lakes, Xochimilco
and Chalco in Mexico City, feeds on zooplankton during its larval stages. We
evaluated the functional response over eight weeks of A. mexicanum fed
different prey items found in its natural habitat (rotifers: Brachionus
havanaensis, B. calyciflorus, B. rubens and Plationus patulus; cladocerans:
Moina macrocopa, Macrothrix triserialis, Alona glabra and Simocephalus
vetulus; and ostracods: Heterocypris incongruens). Zooplankton consumption
by A. mexicanum varied in relation to the prey species and age of the
larvae. Unlike oviparous fish larvae which often feed preferentially on
rotifers in the first few weeks, A. mexicanum larvae fed more on cladocerans
and ostracods. Among the cladocerans offered, larval A. mexicanum consumed
higher numbers of M. triserialis and M. macrocopa. Feeding on the largest
cladoceran tested, S. vetulus, increased after the fifth week. There was a
consistent increase in the number of ostracods Heterocypris incongruens,
consumed with age, from 4 to 169 prey per larva over eight weeks. The
results are discussed with relation to the importance of zooplankton diet in
conservation effort of this endangered species in Lake Xochimilco.