HYPOXIA TOLERANCE IN THE EPAULETTE SHARK (HEMISCYLLIUM-OCELLATUM)

The epaulette shark, Hemiscyllium ocellatum, is a tropical reef shark that can live in an environment with cyclic periods of low oxygen conc entration, suggesting that it has a well-developed capacity for anaero bic metabolism. Most investigations of hypoxia-tolerant teleosts and r eptiles have focused on species that inhabit cold environments. This s tudy was carried out on a tropical reef shark in order to determine wh ether similar strategies for hypoxia survival are used at higher envir onmental temperatures. We studied the effects of a single exposure to mild hypoxia and cyclic exposure to extreme hypoxia on blood-lactate c oncentration and key indicators of neurological function. The basal bl ood-lactate concentration for the epaulette shark was determined as 0. 37 mM and showed a graded increase during hypoxia. After a single expo sure to mild hypoxia (20% of normoxia for 4 h), the mean blood-lactate level rose to 3.07 mM (P < 0.01). After cyclic exposure to extreme hy poxia (eight repetitions of a 120-min exposure at 5% of normoxia), the re was a rise in mean blood-lactate concentration to 5.43 mM (P < 0.00 01). During both hypoxic regimens, there were no observed changes in k ey indicators of neurological function. We conclude that the epaulette shark is tolerant to both mild hypoxia and to cyclic exposure to extr eme hypoxia. (C) 1998 Wiley-Liss, Inc.