The researchers studied how stable isotopes can help identify wild and released populations of Japanese flounder. They analyzed muscle and otolith samples from different groups and found that the δ13C value of the core region of otoliths can distinguish wild from released populations. This method could be useful in identifying broodstocks involved in spawning migration and evaluating the effects of flounder enhancement efforts. The δ18O values of otoliths did not show clear distinctions between populations. This study provides a promising technique for assessing fish populations and replenishing resources.