THE SWIMBLADDER GAS CONTENT OF SOME FRESHWATER FISH WITH PARTICULAR REFERENCE TO THE PHYSOSTOMES

Abstract

Swimbladder gas samples were analyzed from 10 species of fish caught at various depths extending from the surface to 486 ft. in Lake Huron and adjoining waters. The physoclists studied, yellow perch and burbot, had gas compositions which agreed with previous findings. From progressively greater depths, these displayed decreasing nitrogen percentages and increasing oxygen percentages. The physostomes, lake trout, lake whitefish, shallowwater cisco, deepwater cisco, bloater, American smelt, white sucker, and longnose sucker, displayed strikingly high percentages of nitrogen and correspondingly low percentages of oxygen at all depths. Carbon dioxide was found only in traces in both groups. Results of flotation pressures determined for American smelt, shallowwater cisco, and bloater indicated that most specimens were probably buoyant at depths of capture and that results of gas analyses were indicative of the gas compositions at depths of capture. Both physostomes and physoclists from the greatest depths of capture displayed swimbladder nitrogen pressures in excess of 0.8 of an atmosphere, the partial pressure of dissolved nitrogen in most natural waters. The excess was slight in physoclists but in physostomes it was nearly equal to the total (hydrostatic plus atmospheric) pressure.