Factors Influencing the Aerial Breathing and Metabolism of Gars (Lepisosteus)

Several factors influencing the rate of aerial breathing and metabo- lism of young-of-year gars were studied. Without access to atmospheric oxygen, the lethal oxygen concentration was found to be approximately 2.45 mg/1 at 73F. The average rate of oxygen consumption of these fishes was 0.295 ml 0,/gm/hr. Pre- vention of aerial breathing produced no observable ill effects on the gars tested pro- vided the dissolved oxygen content of the water was above 3 mg/1. Undoubtedly, the gar's air bladder serves a hydrostatic function as well as a respiration function, and thus complicates the analysis of aerial breathing of these fishes. The temperature acclimation time of alligator gar, based on the rate of aerial breathing, requires ap- proximately 48 hours. INTRODUCTION. Biologists who first described the habits of Lep- isosteus believed that the swim bladder of this fish preformed a respi- ratory function. This belief was based on several observations: (1) the internal surface of the walls of the swim bladder are cellular and spongy; (2) a rich network of capillaries supplies blood to this organ; (3) a pneumatic duct connects the swim bladder with the pharynx and a glottis is present at this connection; and (4) gars often appear to gulp air. Investigations by Potter (1927) showed that gar could live 20 days in deoxygenated water if permitted to gulp air at the surface. Con- versely, he found that gar could live and apparently remain healthy for several days when confined below the surface, if they were main- tained in oxygenated water. He also demonstrated that there was an exchange of gases in the swim bladder resulting in a decrease in the percentage of oxygen and an increase in the percentage of carbon dioxide between inhalations. From this, he concluded that the swim bladder of Lepisosteus is an organ of supplementary respiration. Working with the longnose gar, L. osseus, and the spotted gar, L. oculatus, Saksena (1963) showed a significant increase in the rate of aerial breathing for both species with a rise in water temperature. He 45