Tuna sleeps. Although they are aquatic animals, they also need to sleep. It's just that tuna don't have eyelids and don't close their eyes when they sleep, so it's difficult to tell whether they are in a state of rest by whether they close their eyes or not.

In addition, the gills of tuna have been degraded, and they don't need to swim constantly to get oxygen. Even if they keep swimming, they will enter a state of rest for a short time. To judge whether they are sleeping, you can observe their swimming speed. Tuna swims very fast when awake, but it will be slower after sleeping, and its metabolism will be slower.

Tuna belongs to marine fish. There are many species of tuna, and different species have different body shapes. The common yellowfin tuna is 1-3 meters long in adulthood. Bluefin tuna will be bigger, and its body length can reach more than 3 meters in adulthood. There is also big-eyed tuna, which will be relatively small in size. In adulthood, the body length is between 1.5 and 2 meters.

In addition to the variety that affects their body shape, the environment in which they live also affects their body shape. If the sea where they live is polluted, their size will also be affected. If they live in comfortable sea areas, they will be bigger.