There are two types of fish farming. In the single generation harvest type, fry are released into the natural population in order to increase the total catch. In the reproductive type, fry are released for the purpose of increasing the number of adult fish capable of spawning, thus increasing the natural population catch in the next generation. In the Iwami Sea area of Shimane Prefecture, the results of flounder releases by the fish farming industry can be thought to be a combination of both the direct effects and reproductive effects.