It is coming to recongnize that the fluctuations in abundance of some pelagic fishes arestrongly affected by the global climate change. To control these fish resource, fisheriesscientists lay stress on interactions between the long-term variationsin fish populations,fishing conditions and their envrionment, recently.The grey mullet(Mugil cephalus) is a marine fish species that wildly distributed between42° North Latitude and 42° South Latitude throughout the world. Besides the locallydistributed grey mullet, there are migrating type of grey mullet fishes that are localizedin the coastal waters of mainland China would migrate to the central or southern part ofthe Taiwan Strait for spawning around the coastal waters of Taiwan from November tonext January . Because of the details on certain biological aspects, such as life-cycle,ecology, population structure, migration paths, and reason for the fluctuation of annualyields are still unknown, we have started carrying out research on the populationstructures and phylogenetic relationships between the grey mullet species in thesurrounding waters of Taiwan.We also want to carry out such works using methodologies in the fileds of biochemistry,such as analysis on isozyme electrophoresis. From the isozyme analysis that the GPI locihave already enabled us to distinguish the migratory grey mullet population from thelocal population.