Tuna, as an extraordinary fish in the ocean, has many unique features.
The body is fusiform in shape, slightly rounded at the front and tapering at the back, a shape that greatly reduces drag when swimming and provides the basis for rapid ocean travel. The tuna's fins are delicately constructed, with the two dorsal fins very close to each other, the first dorsal fin with 11 - 14 hard spines, the anterior end is significantly longer than the posterior end, with a deep concave profile, while the second dorsal fin has 12 - 16 spines. The second dorsal fin has 12 - 16 spines. The dorsal and anal fins have 7 - 10 smaller fins behind each other. Its pectoral fins are large, with 30 - 36 fins, making it one of the largest among fishes. The caudal fin is crescent shaped and creates a strong propulsive force when swinging. In terms of coloration, the dorsum is mostly metallic dark blue, the abdomen is white, and the small fins are bright yellow, with black edges in some species and stripes on the pectoral and abdominal areas.
The internal structure of tuna is also unique. Its skeleton is strong, with an adipose medullary shaft between the dorsal spine and the dorsal fin, which provides strong support and reduces weight. The muscles are plump and rich in meat fibers, which contribute to its excellent swimming ability. Most tuna also have swim bladders, which play an important role in the ionic balance of gases in the body and the insulation of water.
In terms of physiological characteristics, tuna belongs to regional warm-blooded fish, with a special "countercurrent heat exchanger" in its body, which maintains heat with the help of muscle heat production and countercurrent heat exchange vascular network to keep the temperature of key parts higher than the ambient temperature. Its respiration is percussive respiration, due to the gill cover muscles can not be opened and closed, can only open the mouth to continue to swim, relying on the flow of water through the gills to obtain oxygen, once it stops swimming, it will be quickly due to a lack of oxygen and asphyxiation death. These unique characteristics make tuna occupy a unique and important position in the marine ecosystem.