The blackfin tuna fish or thunnus atlanticus are the smallest species of tuna but are very large in number. They are only found in the Atlantic Ocean, and they are less common then normal tuna. They are also known for migrating often to temperate weather locations up and down the Atlantic coast.
This type of tuna has a very interesting muscular system that is comprised mostly of two types of muscle: red muscle and white muscle. The red muscle is the inner most muscle that is close to the lateral retia. 99% of the body heat produced from these muscles are retained by the lateral retia. The red muscles also have a high concentration of veins and arteries passing through it, since it really makes up the center of the fish. Finally, the white muscle is also used for movement and and to produce heat for the rest of the body. The blackfin tuna is mostly composed of this muscle since it takes up the whole outer section of the body.
http://www.flmnh.ufl.edu/fish/Gallery/Descript/BlackfinTuna/BlackfinTuna.html
http://www.fao.org/fishery/topic/16082/en
This type of tuna has a very interesting muscular system that is comprised mostly of two types of muscle: red muscle and white muscle. The red muscle is the inner most muscle that is close to the lateral retia. 99% of the body heat produced from these muscles are retained by the lateral retia. The red muscles also have a high concentration of veins and arteries passing through it, since it really makes up the center of the fish. Finally, the white muscle is also used for movement and and to produce heat for the rest of the body. The blackfin tuna is mostly composed of this muscle since it takes up the whole outer section of the body.
http://www.flmnh.ufl.edu/fish/Gallery/Descript/BlackfinTuna/BlackfinTuna.html
http://www.fao.org/fishery/topic/16082/en