Abstract
The early research on cetaceans was developed from age determination by biological samples, such as growth layers in teeth, growth rings in ear plugs or reproductive organs collected by commercial whaling. Objects of research were shifted to the stranded or captive cetaceans after moratorium of commercial whaling. Captive dolphins have contributed to not only exhibition but also study. The identifiable captive dolphins are more useful for observation and experiment for long terms. The results in research on reproductive biology captive animals can be applied to the wild. It is difficult to study cognitive science in wild and trained captive animals are also available.
