 In contrast to the warm muscle and viscera of swimming bluefin tunas, the heart and gills remain at or near ambient water temperature in all tuna species.Tunas achieve regulation of body temperature by employing complex vascular structures called rete mirabile.In bluefin tuna, large lateral cutaneous vessels that branch off into the arteries and veins of rete mirabile supply blood to the red muscle, instead of a centrally located aorta.