The effect of high CO2 saline ground water on the blood oxygenation properties of the West Australian dhufish was evaluated following ill thrift of wild caught dhufish held in the water The Bohr factor was calculated for whole blood from captively bred dhufish to assess the potential effect of increased pCO2 on oxygenation of dhufish haemoglobin. Blood pH, pCO2, electrolytes and haematological parameters were determined for two groups of captively bred dhufish held long term in seawater and high pCO2 ground water, respectively. Chemical analysis of the two water sources was performed. Ground water in dhufish tanks had a pH of 7.7 (seawater pH 8.1) and pCO2 6.45 mm Hg (seawater 1.50 mm Hg). Dhufish whole blood had a large Bohr factor. Dhufish acclimated to ground water had increased plasma pCO2, HCO3-, haemoglobin content, haematocrit and erythrocyte counts. The increase in haemoglobin content was the result of an increase merythrocytes.