The current propagation systems and physiological studies of Japanese chum salmon

Abstract

In Japan, chum salmon Oncorhynchus keta is mainly propagated via artificial insemination, the release of juveniles from their natal river to the ocean, and the recapture of homing adults along the coast and within the natal river. The biomass of Japanese chum salmon increased steadily from 1970 to 1996 because of the successful improvement of propagation systems. However, the returning rate of homing adults has become unstable, and the aftermath of the 2011 Tohoku earthquake and tsunami caused a major decrease in the number of juveniles released in the Tohoku area. It is now widely accepted that specific factors in the natal stream are imprinted on the nervous system of juvenile chum salmon during downstream migration and that adults use these factors to recognize the natal stream during their upstream homing migration. Recent physiological studies from behavioral to molecular biological approaches to elucidate mechanisms of imprinting and homing migration in chum salmon are useful for developing new chum salmon propagation systems to enhance the survival rates of juveniles in coastal areas and stabilize the returning rate of homing adults. This review introduces a semi-closed recirculating aquaculture system to estimate the health condition and improve the olfactory imprinting capability of juvenile chum salmon.