• Acipenseriformes;
  • bioenergetics modelling;
  • ram ventilation;
  • respirometry;
  • thermal sensitivity

This study quantified the effects of temperature and fish mass on routine metabolism of the American paddlefish Polyodon spathula. Thermal sensitivity, as measured by Q10 value, was low in P. spathula. Mean Q10 was 1·78 while poikilotherms are generally expected to have Q10 values in the 2·00–2·50 range. Mass-specific metabolism did not decrease with increased fish size to the extent that this phenomenon is observed in teleosts, as evidenced by a mass exponent (β) value of 0·92 for P. spathula compared with 0·79 in a review of teleost species. Other Acipenseriformes have exhibited relatively high β values for mass-specific respiration. Overall P. spathula metabolism appears to be more dependent on body mass and less dependent on temperature than for many other fishes. An equation utilizing temperature and fish mass to estimate gross respiration for P. spathula was derived and this equation was applied to respiratory data from other Acipenseriformes to assess inter-species variation. Polyodon spathula respiration rates across water temperature and fish mass appear most similar to those of Atlantic sturgeon Acipenser naccarii and white sturgeon Acipenser transmontanus.