Abstract

Respiratory gas exchange, ventilation, heart rate and acid-base balance were studied in a freshwater euryhaline crayfish and correlated with osmo- and ionoregulation during 48h exposure in 25, 50 and 75% seawater. Despite increases in haemolymph ionic levels some degree of regulation was evident. Respiratory and cardiac frequency decreased in 25 and 50% seawater but were elevated in 75%. Concomitantly O₂ uptake decreased as the medium approached isosmicity with the blood. Blood gas analysis demonstrated reductions in O₂ tension and content but the a-vO₂ content difference was maintained except in 50% SW. An acidosis was measured in 75% seawater which was partially offset by hyperventilatory alkalosis and may have been coupled with the decrease in blood ammonia. Evidence that haemocyanin acts as a source of free amino acids for elevation of osmolality will be presented. The opposing effects of pH and ionic concentrations on the respiratory pigment were assessed: in vivo analysis indicated an increase in 0₂ affinity but the existence of another dialysable cofactor was implicated in vitro. These changes resulted in reduced CO₂ buffering capacity.

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