Originally Posted by
koiman1950
I have been to breeders in Japan that keep fish small as there are many hobbyists in Japan that have very limited space. Like in growing bonsai trees, the key here is simply reducing the environment to restrict growth. Sakazume is one of them and he sells many "bonsai Nisai" especially Goromos. But, I don't know of any breeders who actually have genetically stunted fish. They just keep them in crowded conditions to keep them small. Size isn't everything and is not a indicator based on prices either. Some bonsai koi can be rather expensive relatively speaking. I have seen and know of some hobbyists however, who can actually grow koi in small 1000-1500gal ponds, with a heavy stocking load and still get fish to grow to 25+" as well. It does have something to do with what Kodama stated about Pheromones but I wouldn't reduce the water changes to make this happen.
Yes, there are many varieties of Doitsu fish that do tend to grow slower than their wagoi counterparts, but not always and males, in a small environment would be your best bet as well. As to needing 1000gal/fish to get good growth, this has more to do with growing female fish to very large sizes and for competition mostly. 250gal or more is more the norm for the average hobbyist and 500 is more of the ideal all around number.