Mayer waves in the circulation of a teleost fish

Regular oscillations in arterial blood pressures identical to mammalian Mayer waves were recorded in unanesthetized trout (Salmo gairdneri). The waves were associated with hemorrhage, were caused by fluctuations in systemic vascular resistance, and were sometimes accompanied by fluctuations in cardiac output of opposite phase. Alpha adrenergic blockade eliminated the phenomena; muscarinic cholinergic blockade was ineffective. The existence of Mayer waves provides evidence for a nervous control of vasomotor tone in teleosts.