Conclusions
In conclusion I believe that most fish species behave as oxygen regulators when
exposed to hypoxia within their natural temperature regime, and there are no a priori
reasons why any vertebrate with a significant amount of functional respiratory pigment
and a reasonable matching of ventilation and perfusion at the gas exchange surface should not be able to regulate its standard metabolic rate over a wide range of oxygen
tensions from normoxia to severe hypoxia. The reason that many investigators have
shown T-curves can probably be ascribed to spontaneous activity, handling stress and or
erroneous use of flow-through respirometry. It must be accepted, however, that at least
some of the sturgeons are oxygen conformers when resting, as described by Burggren and
Randall (1978), but may behave as oxygen regulators when allowed to swim at their
preferred swimming speed according to McKenzie et al. (in press). Are there any other
potential oxygen conformers? What about icefish that do not have any red blood cells and
no functional respiratory pigment? Experiments in the near future will hopefully solve
this question