The physiological tolerance of the grey carpet shark (Chiloscyllium punctatum) and the epaulette shark (Hemiscyllium ocellatum) to anoxic exposure at three seasonal temperatures

摘要

The epaulette shark (Hemiscyllium ocellatum) and the grey carpet shark (Chiloscyllium punctatum) are commonly found in periodically hypoxic environments. The ecophysiological time available for these animals to safely exploit these niches during different seasonal temperatures was examined. The time to loss of righting reflex (T (LRR)) was examined in response to an open ended anoxic challenge at three seasonal temperatures (23, 25 and 27A degrees C). Ventilation rates were measured in an open ended anoxic challenge at 23A degrees C and during 1.5 h of anoxia followed by 2 h of re-oxygenation at 23 and 25A degrees C. The mean T (LRR) of epaulette and grey carpet sharks was inversely proportional to temperature. The T (LRR) was similar between species at 23A degrees C; however, grey carpet sharks had significantly reduced T (LRR) at higher temperatures. During the standardised anoxic challenge, epaulette sharks entered into ventilatory depression significantly earlier at 25A degrees C. During re-oxygenation, epaulette sharks exposed to anoxia at 23A degrees C had no significant increase in ventilation rates. However, after anoxic challenge and re-oxygenation at 25A degrees C, epaulette sharks showed a significant increase in ventilation rates during re-oxygenation. Grey carpet sharks displayed no evidence of ventilatory depression during anoxia. However, during re-oxygenation, grey carpet sharks had significantly elevated ventilation rates above pre-experimental levels and control animals. These data demonstrate that the anoxia tolerance times of both species were temperature dependent, with a significant reduction in the T (LRR) occurring at higher temperatures. Epaulette sharks had a significantly greater T (LRR) at higher temperatures than grey carpet sharks, which did not enter into a ventilatory depression.