The metabolic and cardiac responses of cunner (Tautogolabrus adspersus, Walbaum) to temperature fluctuations

The cunner, a marine teleost, exhibits winter dormancy (i.e. becomes inactive and stops feeding) when seawater temperatures fall below 5°C. To examine if this dormant state is associated with active metabolic depression, the effect of season on routine metabolic rate (MRr) and cardiac function was examined in this species. Fish were kept under ambient conditions for a year and their MRr determined at 5 critical seasonal temperatures (5, 9, 14, 5 and 0°C), while cardiac function was determined at the 3 last temperatures (14, 5 and 0°C). Moreover, the ability of cunner to adjust MRr, and cardiac function, when challenged with acute temperature changes was also assessed. This was accomplished by exposing cunner, acclimated to either 5 or 0°C, to a decrease/increase of 5°C, respectively, and maintaining the fish at the final temperature for 3 additional hours. Cunner seasonally depressed MRr and cardiac function, showing high Q₁₀s (> 4) between 5 and 0°C. Further, when subjected to an acute temperature increase (0 to 5°C), dormant cunner rapidly increased both MRr and cardiac function, with high Q₁₀s (> 5). However, when subjected to an acute temperature decrease (5 to 0°C), the cunner were able to actively depress MRr (Q₁₀~8), but not cardiac function, showing a decoupling of the MRr and cardiac response