Tuna is a kind of fish that lives in the ocean. Compared with most other fish, tuna has some very obvious characteristics, such as swimming all the time. If you keep watching them, you will find that they will not stop swimming. In fact, this is because their gills have been degraded in the long process of evolution, they can only keep their mouths open and swim constantly, so that the water can flow smoothly and provide them with oxygen. If they stop swimming, they will die because they can't get oxygen. Therefore, it can be said that they are in a state of swimming throughout their lives.
As mentioned above, tuna need to swim all the time to get oxygen, and they can't stop, otherwise they may suffocate. Many people will conclude that since they are always swimming, they will never sleep and always swim. In fact, tuna need to rest, they will also sleep. It's just that they have a special way of sleeping, which is very different from that of humans and terrestrial animals. For example, humans and many animals can close their eyes. But tuna do not close their eyes, so it is not easy to tell whether they are sleeping or not.
In addition, tuna is different from most fish when they sleep. Most fish will be fixed in one place when they sleep, although their gills will always be in a close, but it can be more obvious that they are sleeping. Tuna, on the other hand, need to swim all the time, and they also swim when they sleep, but the speed of swimming is reduced, and their body uses relatively less energy at this time.
