Abstract: There is provided a method for preventing the occurrence of abnormal behavior such as cannibalism, fright behavior and collision death during rearing, storage and transportation of tuna of larva, juvenile and young adult fish stages, particularly, of those periods in the seed production. The abnormal behavior during rearing, storage or transportation of tuna is prevented by controlling their visual stimuli, particularly, by making wall and bottom surfaces of a rearing water tank coming with contact with the environment transparent, setting a visual stimulus-buffering material through which light transmits partially in both straight and diagonal directions, maintaining the tuna in the presence of colored fine particles in the environment, or controlling the fluctuation in illumination of the environment, or a combination thereof. Alternatively, death of tuna due to collision with a rearing water tank wall is prevented by stimulating their visual sense.