Joryu: Welcome to MFK!!!
I don't know why you think fish will grow smaller in captivity. That may have been true years ago. But, the latest products and information available to the hobby is now showing the opposite to be true. With improved water quality, availability of trace elements, and better and varied diets available, captive fish species are now surpassing their wild sizes. You only have to go as far as the galleries on the many fish sites here and overseas to see larger healthier fish than can be seen in wild caught specimens that have to compete for food and survive in increased levels of pollution.