If you are concerned with introducing any unwanted species along with your minnows, you may want to consider stocking Tuffies, aka Farm-raised Fathead Minnows.
These fish are raised in artificial ponds in Arkansas under very controlled conditions. Tuffies are slightly more expensive, but in certain situations it may be worth the extra money to prevent the accidental introduction of unwanted species.
We recommend stocking about 25 pounds (about 5000 each) per Surface Acre in new ponds without a forage base. Also, if you are stocking minnows when the water is warm, Tuffies can better handle the conditions than regular fathead minnows.