Genetic tagging of released Japanese flounder (Paralichthys olivaceus) based on polymorphic DNA markers

The purpose of this study is to document a genetic profiling approach to track a released hatchery strain of Japanese flounder Paralichthys olivaceus. Microsatellite DNA loci together with nucleotide sequences of the mitochondrial DNA (mtDNA) control region were used as genetic tags. In September 2001, flounder juveniles produced at a hatchery station (Japan Sea-Farming Association (JASFA) hatchery) were stocked into a natural sea area, and at around the same time and within the same area, a different hatchery strain was released by another hatchery station. In this study, we focus on tracking the released flounder produced at the JASFA hatchery, which were profiled with the two classes of molecular marker. A total of 1576 individuals including both wild and released flounder were entrapped in a set net during a 6-month period 1 year after the release (September 2002-February 2003). Of these, the 2001-year-class fish were sorted based on the total lengths (18-34 cm), and further screening to differentiate hatchery-raised fish was made by examining for hypermelanosis on the blind body side, which is a typical phenomenon which occurs in hatchery-raised flounder. Through these processes, 149 individuals were selected as a sample of hatchery fish released by either the JASFA hatchery or the other hatchery. Parental allocation based on the genetic profiles retrieved 35 of the 149 recaptures as survivors of the released JASFA fish. There was no significant difference in the family size distribution between the recaptured JASFA fish and that of juveniles estimated when the JASFA seedlings were released into the sea, suggesting that mortality of the released flounder had not arisen in favor of particular families under the natural environment.