In this paper, the study results on the fish age estimation issues, as an application of the method of digital image
processing, presented by analysis from otolith image. First, a kind of Artificial Neural Network (ANN), the Pulse-
coupled Neural Networks (PCNN), is proposed, and used to identify the different summer or winter year-rings patterns.
Second, a well-founded approach, using morphological features, is brought forwand to automatically detect the nucleus
within the otolith images. Finally, the Morphological Method is used to deduce the fish's age. The results of this paper
maybe significant in fishery research, and the methods can be used in other biologic features identify fields.