1Department of Marine Bioscience, Ocean Research Institute, University of Tokyo, Tokyo 164-8639, 2Toyama Prefectural Fisheries Institute, Toyama 936-8536, 3National Research Institute of Fisheries Science, Fisheries Research Agency, Nagano 386-0031, Japan
We developed a novel single nucleotide polymorphism (SNP) marker on the control region of the mitochondrial genome of the ayu Plecoglossus altivelis; the marker can distinguish nucleotides A or G at a specific nucleotide site at which amphidromous and landlocked stocks of ayu are differentiated by different predominant nucleotides. The mitochondrial SNP marker was used to genetically trace landlocked ayu fish released into the Sho River (Toyama Prefecture) which was also inhabited by a native amphidromous population. Larvae, juveniles, and adults were collected throughout a year from the fluvial and marine habitats within and around the river, and subjected to DNA analysis. Mixing rate of landlocked stock was estimated for each life-stage on the basis of the frequency of the specific nucleotides at the SNP site. Though the estimation suggested considerable loss of landlocked ayu after release, mixing of drifting larvae reproduced by females of landlocked ayu was traced in the early spawning season. However, no evidence of survival in the offspring of the landlocked form was found from fish in the marine stage. The landlocked ayu was confirmed to be ineffective in the stock enhancement by releasing.