Burst swimming in fish results in a marked metabolic acidosis. Chinook salmon (Oncorhynchus tshawytscha) blood was shown to have a marked Root shift, such that burst swimming and the subsequent metabolic acidosis should impair oxygen delivery to the tissues and, therefore, aerobic swimming capacity. Burst swimming was found to have no effect on aerobic swimming capacity in Chinook salmon and it is concluded that any effects on aerobic swimming, of the induced metabolic acidosis following burst swimming, was offset by the release of catecholamines.

This paper describes the design of a modified Brett-type respirometer for use with fish up to 2 kg at swimming speeds as high as 2.5 m·s(-1). Control of the respirometer, experimental monitoring and data acquisition are performed by computer. Water velocity, temperature, pH, dissolved oxygen and carbon dioxide can be controlled at predetermined levels to enable experiments to be conducted over several days with minimal deterioration in water quality.

In vivo experiments were carried out to determine the effect of forced activity on circulating catecholamine levels, haematocrit, and the pH and water content of erythrocytes in the toad, Bufo marinus. In addition, the effect of the beta-adrenergic agonist isoproterenol on erythrocyte pH and water content was examined in vitro. Forced activity caused a significant decrease in both whole blood and erythrocyte pH, while haematocrit and circulating adrenaline and noradrenaline levels increased. Erythrocyte water content did not change following forced activity. Addition of isoproterenol to toad blood in vitro had no effect on either erythrocyte pH or water content. The apparent absence of beta-adrenergic effects on erythrocyte pH and water content in the toad is in sharp contrast to the response of teleost fish erythrocytes to beta-adrenergic stimulation. The significance of these differences is discussed.

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 Po2 varied from 34.5 to 91.7 mmHg, and Pcoco2 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 Po2 and PCOCO2 to rise and pH to fall. Oxygen-combining curves forwhole 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 (ΔlogP50/Δ pH) was −0.59 ± 0.046(30). Unusual features of CO2-combining curves are attributed to a significant Rooteffect. Although these in vitro properties of tuna whole blood are at variance withother published data on tuna they nevertheless substantiate our determinations madein vivo.