This is a ruby fish, which belongs to the family Lepidoptera. This kind of fish is characterized by its strong territory. When it sees weaker fish, its color becomes darker, in order to intimidate and drive away each other. However, when encountering more powerful warship fish and map fish, the body color will not change, so as not to attract attention and be attacked.

The principle of discoloration is the result of the contraction and expansion of pigment cells in the skin, which is controlled by endocrine, so ruby fish is an interesting fish that can express emotions.