THE INFLUENCE OF BLOOD GAS PROPERTIES ON GAS TENSIONS AND pH OF VENTRAL AND DORSAL AORTIC BLOOD IN FREE-SWIMMING TUNA, EUTHYNNUS AFFINIS

We have developed a technique for capture, anaesthetization, instrumentation and release of tuna and have made the first determinations of blood gas values in dorsal and ventral aortae of free-swimming tuna. Dorsal aortic Poj varied from 34-5 to 91-7 mmHg, and Pco2 ranged from 3-7 to 7mmHg. Dorsal aortic blood [pHa = 7-77 ± 0-04 (8), mean ± one S.E.M. (N)] was more alkaline than ventral aortic blood [pHv = 7-65 ± 0-02 (7)]. Warming dorsal aortic blood from 25 to 35 °C in a closed system caused Po^ and PCo2 to rise and pH to fall. Oxygen-combining curves for whole blood were sigmoid [mean Hill's number = 1-72 ± 0-05 (11), range 1-57-2-0] and P50 over the pH range found in free-swimming animals was 21 ±1-75 (8) mmHg. The CO2-induced Bohr coefficient (AlogPs0/A pH) was -0-59 ± 0-046 (30). Unusual features of CO2-combining curves are attributed to a significant Root effect. Although these in vitro properties of tuna whole blood are at variance with other published data on tuna they nevertheless substantiate our determinations made in vivo.