Oral Presentation Australian Society for Fish Biology & Australian Freshwater Sciences Society Conference 2026

Chronic hypoxia exposure improves physiological performance in an iconic dryland river fish (144884)

Holly A Weston 1 , Rebecca L Cramp 1 , Jonathan Marshall 2 , Sherry Zhai 3 , David Hamilton 4 , Adrian Gleiss 5 , Matthew Hipsey 6 , Andrea Prior 7 , Craig E Franklin 1
  1. School of the Environment, The University of Queensland, St Lucia, QLD, Australia
  2. Department of the Environment, Tourism, Science and Innovation, Queensland Government, Dutton Park
  3. UWA School of Agriculture & Environment, The University of Western Australia, Crawley, WA, Australia
  4. Australian Rivers Institute, Griffith University, Griffith, Queensland, Australia
  5. Centre for Fish, Fisheries and Aquatic Ecosystem Research, Murdoch University , Perth, WA, Australia
  6. Aquatic Ecodynamics, UWA School of Agriculture & Environment, The University of Western Australia, Crawley, WA, Australia
  7. Department of Local Government, Water and Volunteers, Toowoomba, QLD, Australia

Background/Aims

Increasing duration and severity of aquatic hypoxia in a changing climate and anthropogenic landscape is a recognised issue for freshwater ecosystems. In Australia, native fish in the Murray-Darling Basin are an important indicator for the health of dryland riverine ecosystems for their role in maintaining ecosystem function, and as organisms at the forefront of changing environmental conditions. During drought conditions, aquatic oxygen levels ranging from moderately hypoxic to anoxic are frequently recorded in the northern Murray-Darling Basin. It is recognised that some fish can offset the negative effects of hypoxia through phenotypic plasticity, however there is still limited understanding of the extent to which this is expressed in key northern Murray-Darling Basin species. This study aimed to investigate the physiological responses of juvenile Murray cod (Maccullochella peelii) to changes in acute and chronic oxygen conditions.

Methods

Murray cod were maintained in tanks 28˚C water to simulate summertime temperatures when hypoxia typically occurs. Differences in metabolism between fish exposed to normoxia (>90% air saturation) or moderate hypoxia (~45% air saturation) for 4 months were evaluated by measuring an aerobic scope curve and metabolic enzyme activity.

Results

Chronic exposure to moderate hypoxia was shown to increase aerobic scope at low levels of oxygen compared to fish only acutely exposed to hypoxia. This was associated with an increase in spleen mass, a red blood cell reservoir, which may have improved oxygen carrying capacity in hypoxic conditions. Despite improvements in aerobic performance, M. peelii growth and appetite remained suppressed in chronic hypoxic conditions.

Conclusions

Our findings indicate that while M. peelii are well adapted to survive in moderately hypoxic environments, extended exposure to hypoxic conditions may limit the ability of individuals to reach the large sizes that the iconic species is known for.