Printed in Great Britain ON THE RESPIRATION OF THE KILLIFISH

It has been shown that many factors are involved in determining the metabolic rate of an individual fish (Fry, 1957; Hughes & Shelton, 1962). The rate of respira-tion, for example, is influenced not only by environmental factors such as temperature and the concentration of dissolved oxygen and carbon dioxide, but also by such complicated physiological and ecological features as the size, activity and history of the fish, and external stimuli, e.g. light and sound. It was one of the main purposes of the present investigations to consider these aspects of fish respiration. A reduction of external stimuli was achieved by keeping the fish in darkness and in a constant-temperature room. Most measurements were recorded remotely in order to avoid effects due to the presence of an experimenter in the room. It is known that the gills of marine fishes show wide variations in their gill areas (Gray, 1954). Measurements of gill dimensions in many species of fish, and determina-tion of the relationship between body size and gill area within single species have also been made (e.g. Hughes, 1966,1970, 1972; Muir & Hughes, 1969). It is of interes