Control and coordination of gas transfer in fishes

Abstract

Recent developments pertaining to the control and coordination of gas transfer in fishes have been reviewed. Gill ventilatory water flow can markedly affect blood respiratory and blood acid–base status. Although arterial oxygen content traditionally has been considered the predominant factor controlling ventilation, we present evidence for additional involvement of both blood acid–base status and circulating catecholamines. An analysis of the independent effects of blood oxygen content, acid–base status, and catecholamines in controlling ventilation is confounded by the interrelationships among these variables. It is likely, however, that each factor is involved to some extent in ventilatory control in fishes. Blood oxygen transport is affected by the carrying capacity of the blood and red blood cell chemical status. Blood oxygen-carrying capacity is increased during periods of stress by adrenergic release of red blood cells from the spleen. Concurrently, adrenergic stimulation of red blood cell Na+–H+ exchange, reduction of intracellular nucleoside triphosphates, swelling of red blood cells, and respiratory alkalosis all tend to increase oxygen affinity and capacity of hemoglobin. Results of recent in vivo studies indicate that adrenergic inhibition of plasma bicarbonate dehydration may contribute to the respiratory acidosis after exhaustive exercise in fishes. Evidence is presented to show that hypoxemia, rather than blood acidosis per se, is the proximate stimulus for catecholamine mobilization during periods of stress in fishes.