The trajectory of fish is an important index reflecting the behavioral characteristics of fish, which provide important information for studying the living habits of fish. In this chapter, two color RGB cameras were used to build the shooting platform to film the fish’s long-term motion. Through preprocessing, background interframe difference, three-dimensional reconstruction, and other methods, the three-dimensional trajectory of the fish was obtained, and the behavior characteristics of the fish were analyzed and studied. We found that fish have phototaxis, prefer to swim in mild light and the surrounding environment close to the impact of objects; and have tendency to edge, prefer to swim around and stick the tank. Moreover, the fish have a tendency to deepen and are accustomed to staying in the underwater environment below 0.25 m. Through long-term monitoring, we also found that fish have indirect “resting” behaviors similar to those of human beings around 8:00, 14:00, and 21:00. The purpose of this study is to expand the research on ornamental fish culture and fish behavior.