Fish migrations are an important characteristic of the Mekong River. Many species need to move between freshwater and marine waters between Mekong countries as either adults or juveniles to complete their life cycle known as diadromous fishes. Unfortunately, migration behaviors of diadromous species have very limited information and unlikely pay enough attention to this group, this can lead to poor management and extinction. In addition, the persistence of these species is threatened by a series of dams planned across the Mekong Basin by blocking their migration routes. There is subsequently a pressing and urgent need to improve the understanding of fish migration so that they can be considered as part of dam development planning in the Lower Mekong Basin. A review shows that many Lower Mekong fish species reside in a wide range of salinities. At least one hundred fish species exhibit diadromous traits. But a literature review alone is insufficient to determine diadromy; hard data is required. Some of these species were subsequently selected for otolith microchemistry analysis. Trace elements are used as proxies to reconstruct their historical habitat experiences. Moreover, water is also sampled to check trace metals in different locations in the basin. Preliminary results indicate that many more Lower Mekong species are diadromous than previously thought.