As the goldfish is a common experimental animal for vision research, including psychophysical behavior, it is very important to quantitatively score fish behavior. We have previously developed a computer image processing system which can acquire the positional coordinates of goldfish moving freely in an aquarium and determine turning directions (go straight, right or left turn). In the present study, an algorithm to determine tilting angles of moving goldfish was constructed. We also made histograms for quantifying the interaction between pairs of goldfish (two-point distance). By using these histograms, we estimated the time-course of behavioral regeneration after optic nerve transection in goldfish. Control goldfish showed an equal percentage of right or left turns and maintained an upright position in a dorsoventral axis. When the optic nerve of a goldfish was unilaterally sectioned, the goldfish showed predominant turning and slight tilting toward the intact eye. The abnormal turning and tilting behaviors lasted for 10-14 days and then gradually decreased, returning to control behaviors by one month after the unilateral transection. When the optic nerve of a single goldfish was bilaterally sectioned, it did not show any preferential turning and tilting behavior, which is similar to what was observed in control goldfish. However, the trace maps showed that, after bilateral sectioning, fish preferred to cross the center of the tank, which was unlike control fish. In control pairs, one goldfish chased the other with a fixed small range of two-point distances. However, in pairs of goldfish with bilateral transection of the optic nerve, the blind goldfish behaved independently of each other, with a long two-point distance. The long two-point distance of the blind goldfish lasted for at least two months and then slowly returned to control two-point distance by four months after bilateral transection. Such fast and slow recovery in goldfish behaviors evoked after unilateral and bilateral transection of the optic nerve is discussed with respect to reconnection of regenerating optic nerves in the fish central nervous system. This computer image processing system is a useful tool with which we can quickly and easily quantify fish behavior.