Circulation, oxygen transport, and activity in the crayfish

Area of Science:

• Crustacean physiology
• Respiratory gas exchange
• Comparative physiology

Background:

• Hemocyanin is the primary oxygen carrier in many invertebrates, including crayfish.
• Understanding oxygen transport is crucial for determining the limits of activity in aquatic animals.

Purpose of the Study:

• To investigate oxygen transport and uptake in crayfish (Pacifastacus leniuculus) during varying activity levels and temperatures.
• To determine the factors limiting oxygen uptake and activity scope.

Main Methods:

• Measurements of heart rate, ventilation frequency, oxygen uptake, hemocyanin concentration, and blood oxygen partial pressure (PO2) and pH.
• Use of N-ethylmaleimide as an anticoagulant for hemolymph sampling.
• Estimation of hemocyanin oxygen saturation, cardiac output, and stroke volume using measured parameters and the Fick principle.

Main Results:

• Postbranchial hemolymph PO2 was low (9-12 Torr) after routine activity, with hemocyanin saturation of 55-75%.
• Maximal activity further reduced PO2 and hemocyanin saturation.
• High cardiac output was observed, but ventilation appeared to be the limiting factor for oxygen uptake.

Conclusions:

• Hemocyanin in crayfish is generally not fully saturated with oxygen, even during routine activity.
• Ventilation, rather than circulation, limits the scope for activity in crayfish at different temperatures.
• These findings highlight the critical role of ventilation in crustacean respiratory physiology.