Lucy Sudekum and Colin Townes-Anderson
Development of the Migration
Spawning usually occur in the warmer waters of Mexico and the Mediterranean for Atlantic bluefin tuna, with females having the ability to lay up to 30 million eggs. The bluefin tuna begin to develop within 2-3 days and begin to feed. As colder months approach, the tunas move to colder waters to begin feeding . These fish once again return later in their lives to spawn in Mexico and the Mediterranean. (Teo et al.) The bluefin tuna begins to migrate at around one to two years, as demonstrated by Kitagawa et al 2009. These tuna crossed the nothern Pacific, traveling 8,000 km, possibly for food.
Development of Endothermy and Heat Retention
Kubo has suggested bluefin tuna are able to produce more heat as they get older, possibly due to increased muscle mass. He showed showed that fish with a fork length (fork length is defined from mouth of fish to split in tail) less than 20 cm cannot maintain a red-muscle temperature above ambient temperature of the water while a bluefin tuna larger than 20 cm can. He suggested that endothermy can be first evidenced between 17-18 cm in juvenile bluefin tuna. Kubo also demonstrated that the body heat transfer coefficent, or the rate at which the fish can heat itself, dropped as the tuna grew larger. (Kubo et al. 2008) Kitagawa suggests that the tuna gradually change their thermoconservation ability in their body as they grow because the peritoneal cavity becomes thicker with growth. Increased "thermal ineritia" results in greater insulation and better temperature stability. Even though this does increase the change of overheating, Kitagwa concludes that because ambient temperatures are cool enough, these fish are able to swim actively in colder temperatures. (Kitagawa et al. 2006)
Figure 2. Chart (a) shows the relationship between fork length (measure from the stout to the middle of the forked tail) and body heat transfer coefficient. Chart (b) shows relationship between thermal difference of the ambient water and the fish's own body heat and the fork length of the fish. (Kubo et al. 2008)