Basic concepts relevant to heat transfer in fishes, and their use in measuring the physiological thermoregulatory abilities of tunas

Abstract

SynopsisAerobic heat production and heat loss via the gills are inexorably linked in all water breathing teleosts except tunas. These processes are decoupled in tunas by the presence of vascular counter-current heat exchangers, and sustained (i.e., steady state) muscle temperatures may exceed water temperature by 10" C or more in larger individuals. The presence of vascular counter-current heat exchangers is not clearly advantageous in all situations, however. Mathematical models predict that tunas could overheat during strenuous activity unless the efficacy of vascular heat exchangers can be reduced, and that they may be activity limited in warmer waters. Tunas may likewise be forced out of potentially usable habitats as they grow because they have to occupy cooler waters. Vascular counter-current heat exchangers also slow rates of heating and cooling. A reduced rate of muscle temperature decrease is clearly advantageous when diving into colder water to chase prey or avoid predators. A reduced rate of heat gain from the environment would be disadvantageous, however, when fish return to the warmer surface waters. When subjected to changes in ambient temperature, tunas cannot defend a specific body temperature and do not thermoregulate in the mammalian sense. Yet when appropriately analyzed, data taken under steady state and non-steady state conditions indicate that tunas are not strictly prisoners of their own thermoconserving mechanisms. They apparently can modify overall efficiency of their vascular counter-current heat exchangers and thus avoid overheating during bouts of strenuous activity, retard cooling after diving into colder water, and rapidly warm their muscles after voluntarily entering warmer water. The exact physiological mechanisms employed remain to be elucidated.

The First Record of Peritoneal Cavity Temperature Recording in Free-Swimming Dolphin Fish Coryphaena hippurus by Using Archival Tags, on the East Coast of Taiwan

“…To examine the response of the peritoneal cavity temperature to variations in the ambient temperature, we used the heat budget model [11][12][13]. The equation for the peritoneal cavity temperature…”

Moving with the beat: heart rate and visceral temperature of free-swimming and feeding bluefin tuna

“…Additionally, Korsmeyer et al (1997a) provided f H data to support the fact that the tuna heart is outside the area warmed by vascular heat exchangers and is thus directly influenced by ambient water temperature (e.g. Carey et al 1984;Brill et al 1994;Fudge & Stevens 1996).…”

“…This statement encapsulates the inherent difficulties associated with examining cardiorespiratory function in the most active and highly evolved predatory fishes in the ocean, the tuna. Tuna can grow to 680 kg in mass and 3.5 m in length, they must swim continuously to ram ventilate their gills and maintain hydrodynamic lift, they can reach burst swimming speeds of approximately 70 km h K1 , and they use vascular heat exchangers to maintain regions of their body at temperatures up to 208C above ambient seawater ( Walters & Fierstine 1964;Carey & Gibson 1983;Collette & Nauen 1983;Wardle et al 1989;Brill et al 1994;Fudge & Stevens 1996). The difficulties of working with tuna are compounded because they are expensive to acquire, difficult to maintain in captivity, and relatively few are available for study (Brill & Bushnell 2001).…”

Development of integrated habitat indices for bigeye tuna, Thunnus obesus, in waters near Palau

“…The distribution and movement of tunas are affected by many environmental variables (Hanamoto1987; Holland et al 1992;Brill et al 1994). Many studies have focussed on the influences of environmental variables, such as temperature, salinity, Chlorophyll a, dissolved oxygen and the abundance of micronekton on the distribution and movement of T. obesus (Dagorn et al 2000;Bertrand et al 2002;Evans et al 2008).…”