Fig. 3. Effects of ambient temperature and speed on bluefin tuna _O2 and tailbeat frequency (TBF). (A) _O2 measurements at swim speeds of 0.75–1.75 BL s^–1 were repeated at three steady-state temperatures on three consecutive days. A significant interaction of temperature and speed effects on _O2 was observed (ANOVA, P<0.05). _O2 increased with swimming speed at 20 and 25°C (P<0.001), but was unaffected by speed at 8°C (P=0.89). Data shown are means ± s.d. of _O2 measurements from three individual bluefin tuna (mass=8.1±0.6 kg). (B) Tailbeats were counted as bluefin swam at speeds of 0.75–1.75 BL s^–1 at temperatures of 8, 20 and 25°C. Both temperature and speed had significant effects on TBF (P<0.001). Data shown are means ± s.d. of TBF counts from three individual bluefin tuna (mass=8.1±0.6 kg).