The reasons are as follows.

1. You can tell the age of the turtle on its belly. There is a gray mark on the bottom plate. The older the turtle is, the darker the color is, which means it is an old fish. The gray mark on the bottom plate of smaller turtles is not so deep.

2. The health of the turtle can be seen by looking at the belly. Whether the belly is smooth and spotless. A turtle with scars indicates that it has been sick. A turtle with blood spots indicates that it is still sick. A turtle with bloodshot eyes indicates that it is still sick. It's been a while since I caught it, or there may be other problems.