Intrinsic vasomotion in the dogfish gill.

It has been reported that fish may match the extent of their respiration to their need for gaseous exchange by failing to ventilate certain gills. One third of the respiratory movements of the lamprey (Lampetra fluviatUis), when in oxygenated tap water, consist of contractions of the anterior two or three branchial chambers only. In partially deoxygenated water the anterior five and finally all of the branchial chambers become active (Wikgren, 1953). In Raja baits water is taken in through the spiracles during rest and perfuses only the anterior four gill pouches. When swimming, water enters through the mouth as well and perfuses the posterior gills (Darbishire, 1907). The dogfish Scyliorhinus camcula has a similar division of the spiracular and buccal inflows between the anterior and posterior gills (Hughes, i960). In the eel, van Dam (1938) reports that during rest only the gills of one side may be ventilated. As the gill circulations are in parallel the possibility exists that venous blood may pass unchanged through the unventilated gills and into the dorsal aorta there to lower the tension of oxygen in the blood passing to the tissues. The mammalian lung also consists of many respiratory units in parallel but failure to ventilate part of it does not cause systemic hypoxaemia because alveolar perfusion is precisely matched to alveolar ventilation. This adjustment is largely effected by the changes in vascular resistance that are mechanically imposed by changes in intrathoracic pressure. However, anoxia itself causes pulmonary vessels to constrict both in the intact mammal and in the isolated lung, and Fishman (1961) concludes, in his extensive review of the subject, that this constitutes a fine control mechanism that shunts the blood from poorly ventilated to well ventilated areas. The possibility exists that a similar mechanism operates in fish so that local anoxia causes a rise in vascular resistance and a diversion of blood to better ventilated gills. Some findings on the response of the branchial vessels of the dogfish to anoxia are presented in this paper; a brief report of this work has already been published (Satchell, 1961a).