Mass movements of fish from one place to another on a regular basis are common and such migratory behavior can range in occurrence from seasonal to daily. Studies of fish migrations are generally of two kinds: those that set out to describe the migrations and those that attempt to explain them. Descriptive work deals with the overall pattern of migratory history as determined using mark-recapture, biotelemetry, micro data recording tags, and elemental analyses of hard tissues such as the otoliths, scales and spines of fish. Mark-recapture studies of fish started on a large scale between 1890 and 1900, and these studies have been one of the best ways of following the migrations of fish by analyzing the distribution of the recoveries of tagged or marked individuals. However, the track taken by the fish during migration is unlikely to be a straight line, and therefore it is difficult to determine the exact migration route. Recently, technological developments in biotelemetry and micro data recording tags have made it possible to trace the migratory history of fishes, including external and internal information recorded simultaneously as digital data. However, those methods are restricted by several limitations. For biotelemetry, there is the difficulty of tracking in rough seas or bad weather, the difficulty of tracking over long periods of time, and the frequent loss of the transmitter signal. For mark-recapture methods and micro data recording tags, recovery of the fish after tagging must be made. With smaller individuals such as larvae and juveniles, the elemental composition of hard tissues, especially in otoliths, has been used to provide valuable information on the temperature and salinity of the migratory environment experienced by each fish throughout its life history. All these methods have certain limitations that are clear when they are examined in detail and the advantages and disadvantages of each can then be evaluated and the best methods can be selected for studying the migration of each life history stage of fishes.
