ABSTRACT
The pumping mechanism maintaining water flow across the gills has been investigated in the trout using pressure transducers and ciné analysis (Hughes & Shelton, 1957, 1958). It was shown that the mechanism could be considered as being made up of a buccal pressure pump and opercular suction pumps, the two being separated functionally by the gill resistance. In this species, Salmo gairdneri, the relative contribution of the two pumps appeared more or less equal, as judged by the areas of the corresponding phases of the differential pressure across the gills. Further studies of the respiratory pumps with special reference to their muscular basis were made using electromyography (Ballintijn & Hughes, 1965) and emphasized the many couplings between the two pumps. Although several studies have been made on the influence of environmental changes on gas exchange (Randall, Holeton & Stevens, 1967), no detailed account has been published on the modifications that occur in gill ventilation mechanisms and interactions with cardiac cycles when trout are subjected to stress. The present series of experiments forms part of such a study in which electrocardiograms were obtained simultaneously with electrical recordings from parts of the respiratory neurones in the medulla, from some respiratory muscles, and with pressure recordings from the buccal and opercular cavities. All were carried out during subjection of rainbow trout to warming thermal stress. A preliminary report of this work has already been given (Roberts & Hughes, 1967).
