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 degrees C. To examine whether this dormant state is also associated with active metabolic depression, the effect of season on routine metabolic rate (MRrout) was measured at five different times throughout the year: early spring (5 degrees C), late spring (9 degrees C), summer (14 degrees C), late fall (5 degrees C), and winter (0 degrees 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 MRrout and cardiac function when challenged with acute temperature changes was assessed. The cunner actively depressed MRrout between fall and winter as temperature fell from 5 degrees to 0 degrees C (Q(10) = 10.4). In addition, MRrout showed a substantial but smaller Q(10) (4.3) when the MRrout at 0 degrees C (winter) was compared with the value recorded during the previous spring at similar to 5 degrees C. These seasonal changes were essentially mirrored by the response of MRrout to acute 5 degrees C increases and decreases in temperature. Similar to MRrout, cardiac output (Q) decreased dramatically as temperature fell from 5 degrees C (fall) to 0 degrees C (winter) in the seasonal study (Q(10) = 7.9) and increased substantially when temperature was acutely increased from 0 degrees to 5 degrees C (Q(10) similar to 5). However, when subjected to an acute temperature decrease (from 5 degrees to 0 degrees 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 MRrout when 5 degrees C seasonally acclimated cunner are exposed to an acute temperature decrease to 0 degrees C.