In situ cardiac performance of Pacific bluefin tuna hearts in response to acute temperature change

This study reports the cardiovascular physiology of the Pacific bluefin tuna (Thunnus orientatis) in an in situ heart preparation. The performance of the Pacific bluefin tuna heart was examined at temperatures from 30degreesC down to 2degreesC. Heart rates ranged from 156 beats min(-1) at 30degreesC to 13 beats min(-1) at 2degreesC. Maximal stroke volumes were 1.1 ml kg(-1) at 25degreesC and 1.3 ml kg(-1) at 2degreesC. Maximal cardiac outputs were 18.1 ml kg(-1) min(-1) at 2degreesC and 106 ml kg(-1) min(-1) at 25degreesC. These data indicate that cardiovascular function in the Pacific bluefin tuna exhibits a strong temperature dependence, but cardiac function is retained at temperatures colder than those tolerated by tropical tunas. The Pacific bluefin tuna's cardiac performance in the cold may be a key adaptation supporting the broad thermal niche of the bluefin tuna group in the wild. In situ data from Pacific bluefin are compared to in situ measurements of cardiac performance in yellowfin tuna and preliminary results from albacore tuna.