Heart rate responses to temperature in free-swimming Pacific bluefin tuna (Thunnus orientalis)
journal contribution
posted on 2023-05-18, 13:20authored byClark, TD, Farwell, CJ, Rodriguez, LE, Brandt, WT, Block, BA
The bluefin tuna heart remains at ambient water temperature (Ta) but must supply blood to warm regions of the body served by countercurrent vascular heat exchangers. Despite this unusual physiology, inherent difficulties have precluded an understanding of the cardiovascular responses to Ta in free-swimming bluefin tunas. We measured the heart rate (f(H)) responses of two captive Pacific bluefin tunas (Thunnus orientalis; 9.7 and 13.3 kg) over a cumulative period of 40 days. Routine f(H) during fasting in the holding tank at a Ta of 20°C was 45.1±8.0 and 40.7±6.5 beats min(-1) for Tuna 1 and Tuna 2, respectively. f(H) decreased in each fish with a Q10 temperature coefficient of 2.6 (Tuna 1) and 3.1 (Tuna 2) as Ta in the tank was slowly decreased to 15°C (~0.4°C h(-1)), despite a gradual increase in swimming speed. The same thermal challenge during digestion revealed similar thermal dependence of f(H) and indicated that the rate of visceral cooling is not buffered by the heat increment of feeding. Acutely decreasing Ta from 20 to 10°C while Tuna 1 swam in a tunnel respirometer caused a progressive increase in tail-beat frequency and oxygen consumption rate (M(O2)). f(H) of this fish decreased with a Q10 of 2.7 as Ta decreased between 20 and 15°C, while further cooling to 10°C saw a general plateau in f(H) around 35 beats min(-1) with a Q10 of 1.3. A discussion of the relationships between f(H), and haemoglobin-oxygen binding sheds further light on how bluefin cardiorespiratory systems function in a changing thermal environment.
History
Publication title
Journal of Experimental Biology
Volume
216
Issue
Part 17
Pagination
3208-3214
ISSN
0022-0949
Department/School
Institute for Marine and Antarctic Studies
Publisher
Company Of Biologists Ltd
Place of publication
Bidder Building Cambridge Commercial Park Cowley Rd, Cambridge, England, Cambs, Cb4 4Dl