On the respiration of Torpedo marmorata.

1. The oxygen consumption of resting Torpedo marmorata was measured using three different methods. The results indicate that this species has a much lower oxygen consumption than other elasmobranchs of comparable size. 2. The gills are ventilated by a mechanism similar to that of other rays, but a relatively small spiracular opening seems to be associated with a more important role of the oro-branchial pump. During hypoxia there is a marked increase in both frequency and amplitude of the ventilatory movements. 3. The frequency of the heart beat is low and shows little change during hypoxia, except under extreme conditions when bradycardia occurs. 4. In some individuals, coupling between cardiac and ventilatory pumps is relatively low but seems to increase at lower ventilatory frequencies and when the ratio between the ventilatory and cardiac frequencies is a whole number. 5. Extreme hypoxia can be withstood for many hours but eventually the ventilatory rhythm ceases; it does not recommence immediately following a rise in ambient oxygen tension. 6. The blood has a low oxygen-carrying capacity and a high affinity. 7. The surface area of the gills is smaller than that of other species that have been investigated, but the quantity of oxygen transferred/unit surface area is similar to that known for other species. 8. It is concluded that Torpedo is a sluggish fish adapted to conditions of low oxygen, but the conditions under which this occurs remain to be determined.