Fig. 6. Species-specific differences in heart rate (A), duration of contraction T_DC (B) and activity of myofibrillar ATPase of atrial muscle (C) between cold-acclimated (4 °C) rainbow trout, cold-acclimated (4 °C) crucian carp and cold-adapted (1 °C) burbot. Dissimilar letters indicate statistically significant differences (P<0.05) between species. Values are means ± S.E.M. of 5-7 preparations as indicated. The data for myofibrillar ATPase activity (C) of rainbow trout and crucian carp are from Aho and Vornanen (1999) and Tiitu and Vornanen (2001), respectively.