The Effects of Oxygen Supply, Epinephrine, and Acetylcholine on the Distribution of Blood Flow in Trout Gills

Injecting vitally stained blood cells into the ventral aorta of unrestrained, cannulated fish, and rapid freezing in liquid nitrogen, permitted the examination of the effects of oxygen supply, epinephrine and acetylcholine on branchial lamellar perfusion. Compared to the conditions in resting fish in air-saturated water, hypoxia and injection of epinephrine significantly increased the proportion of secondary lamellae receiving stained cells, and acetylcholine caused a significant reduction, but hyperoxia did not significantly affect the proportion of lamellae containing stained cells. Perfusion of the filamental central compartment was not affected by the treatments. It is concluded that trout can respond to changes in oxygen supply by varying the number of secondary lamellae perfused with blood, and that the distribution of blood flow is regulated by cholinergic and adrenergic receptors. It is suggested, however, that lamellar recruitment would not be useful in minimizing the costs of osmoand iono-regulation.