User:Kalerg2/sandbox

Physiological Challenges
Southern bluefin tuna are thermo-conserving and can function over a wide range of temperature environments, which allows them to dive from the surface to depths of 1000 m in only a few minutes. Southern bluefin tuna forage in temperate waters of the southern hemisphere oceans, during winter in Australia, and migrate to tropical areas in the north-western Indian Ocean, from spring to autumn, for the spawning season. Their proffered temperature range is 18-20 °C, with most of their time spent below 21°C (91%). Southern bluefin tuna experience a range of ambient water temperatures from a minimum of 2.6° to a maximum of 30.4°. All species of tuna are reported to spawn in water temperatures above 24 °C (Schaefer, 2001) However, 24°C is outside or at the upper limit of temperature tolerances for bluefin tunas. Large SBT have been found to withstand temperatures of less than 10° degrees and as low as 7° for over 10 hours, possibly to search for prey. During the day they migrate through depths of 150-600m, but at night stay in waters that are 50 m or less in depth.

Heat exchange in southern blue fin tuna is a unique adaption among teleost fishes. They are endotherms, which means that they can maintain their internal temperatures elevated above water temperatures, through internally generated metabolic heat even though, heat loss is caused by heat transfer throughout the whole body surface and gills. This is an adaptive feature because it is far more difficult for an organism to maintain a temperature differential with its environment in water than in air. Furthermore, it allows tunas to have faster metabolic reactions, to be more active, and can exploit colder environments. However, a disadvantage is that they have a high energy input and require insulation, and there is potential for greater heat loss because of the high temp gradient with the environment. In order to reduce heat loss Southern bluefin tuna have reduced their heat conduction by the presence of oxidative muscle tissues and fat, as muscle and fat have low heat conductivity, according to Fourier’s law of heat conduction. Their heat convection is also reduced. Since the heat transfer coefficient depends on an animal’s body shape, tunas increased their body size, adopted a fusiform shape, and their internal tissue arrangement is based on different thermal conductance’s.