5. Conclusions
Using a new bimodal intermittent-closed respirometry, we demonstrate
that P. hypophthalmus has a high capacity for aquatic respiration,
being able to survive without air-breathing in normoxic water, and that
it can be characterized as a facultative air-breather. Aerial respiration is
negligible in normoxia, and these data therefore indicate that surfacing
in this species may be reduced in well-aerated conditions. The
possibility of reducing air-breathing frequency would probably be
energetically beneficial for the fish, leavingmore of the aerobic scope for
growth and other activities, due to the proposed energetic costs of
surfacing behavior.
Acknowledgments
This study was performed at Can Tho University (Vietnam) as part of
the PhysCAM-project supported by Danida (Danida Fellowship Centre,
Denmark).