Fish stocking restrictions (and invasive plant laws) are based on their inevitable movement. If you use a chemical in your pond, you are under the same regulations as a farmer that sprays a herbicide. If it damages my property, then you pay. Same goes if your livestock pollute water off your property. These laws have been in effect a very long time. Fish movement is similar to raising sweet corn. If the pollen from field corn fertilizes sweet corn, then the product quality goes down, but it is the responsibility of the sweet corn grower to isolate his crop. You cannot keep the farmer next door from raising field corn or win in court for normal pollen flow (although this has been tested in the courts). Same goes for those producing crop seeds.
