The metabolic response to hypoxia and emersion of aestivating fishes (Lepidogalaxias salamandroides and Galaxiella nigrostriata) and a non-aestivating fish (Bostockia porosa) from south-western Australia

Abstract

We measured the metabolic rate of three fishes (Lepidogalaxias salamandroides, Galaxiella nigrostriata, Bostockia porosa) that are endemic to the south-west of Western Australia. The first two species have been reported to aestivate, the third does not aestivate when the ponds dry up in late summer. For normoxic conditions, the metabolic rates of B. porosa and G. nigrostriata in water (0.48 mL g^–1 h^–1 and 0.44 mL g^–1 h^–1 respectively), are significantly higher than in air (0.21 mL g^–1 h^–1 and 0.08 mL g^–1 h^–1 respectively) but for the more benthic and terrestrially mobile L. salamandroides there was no significant difference between V_O2 in water (0.29 mL g^–1 h^–1 ) and air (0.18 mL g^–1 h^–1). Progressive hypoxia (12, 5 and 2% O₂) decreased the metabolic rate of G. nigrostriata and B. porosa in both water and air but there was a reduction in metabolic rate for L. salamandroides only in water. The metabolic physiology of L. salamandroides in water and air is consistent with the capacity to aestivate in moist soil, but the different metabolic response of G. nigrostriata suggests that it adopts a different strategy to L. salamandroides to survive when the ponds dry up in summer. The metabolism of G. nigrostriata in air and water declines with progressive hypoxia (from 12 to 5 to 2% O₂). B. porosa does not appear to be able to cope metabolically when out of water or under hypoxic conditions, and therefore would not be able to aestivate.