The significance of the nest-building of the nine-spined stickleback, Pungitius pungitius.

The reproductive behavior of the stickleback is unique and odd, occurring inevitably with nesting. However, upon investigation, it has been found that nesting is an obstacle to hatching. The author conducted a survey in the necessity of nesting behavior in the nine-spined stickleback, Pungitius pungitius, and reached following conclusion: For Pungitius pungitius, nesting is the means of communicating to descendants settlement at a fixed area where cold water flowed bountifully and the water temperature was constant. Pungitius pungitius has evolved a behavior pattern that involves settling where water temperature is uniform, without evolving physiologically or morphologically, thereby enabling Pungitius pungitius to adapt to the changes in environment.