Some Aspects of Gas Exchange in Tuna*

Abstract

Some aspects of gas exchange in restrained skipjack tuna were analysed. The average rate at which water flowed over the gills was 2·8 1/min.kg. The concentration of oxygen in water entering and leaving the gills was measured and used to calculate oxygen uptake (692 mg/h.kg) and utilization (0·71). The drop in hydrostatic pressure as water flowed over the gills was 1·9 cm water and agrees favourably with theoretical predictions. The partial pressure of oxygen was measured in blood afferent and efferent to the gills and used to calculate effectiveness of oxygen removal from the water (90%) and the transfer factor for oxygen (0·12 ml/min.kg.mmHg). The average utilization measured in free-swimming tuna was 0·56. The extraordinary ability of tuna to efficiently extract oxygen from the water at high gill water flow rates is discussed.