Metabolic and cardiac responses of cunner Tautogolabrus adspersus to seasonal and acute changes in temperature.

The cunner is a marine teleost that exhibits winter dormancy (i.e., becomes inactive and stops feeding) when seawater temperatures fall below 5°C. To examine whether this dormant state is also associated with active metabolic depression, the effect of season on routine metabolic rate (MR(rout)) was measured at five different times throughout the year: early spring (5°C), late spring (9°C), summer (14°C), late fall (5°C), and winter (0°C). In addition, cardiac function (cardiac output, heart rate, and stroke volume) was measured at the last three measurement time points, and the ability of fall- and winter-acclimated cunner to adjust MR(rout) and cardiac function when challenged with acute temperature changes was assessed. The cunner actively depressed MR(rout) between fall and winter as temperature fell from 5° to 0°C ([Formula: see text]). In addition, MR(rout) showed a substantial but smaller Q(10) (4.3) when the MR(rout) at 0°C (winter) was compared with the value recorded during the previous spring at ∼5°C. These seasonal changes were essentially mirrored by the response of MR(rout) to acute 5°C increases and decreases in temperature. Similar to MR(rout), cardiac output (Q) decreased dramatically as temperature fell from 5°C (fall) to 0°C (winter) in the seasonal study ([Formula: see text]) and increased substantially when temperature was acutely increased from 0° to 5°C ([Formula: see text]). However, when subjected to an acute temperature decrease (from 5° to 0°C), the Q(10) for Q was only approximately 2-3. These results show that (1) cunner actively depress their metabolism in the fall and winter and that this is associated with a large decrease in cardiac function and (2) there is a decoupling between Q and MR(rout) when 5°C seasonally acclimated cunner are exposed to an acute temperature decrease to 0°C.