Both species are native to your area, so introducing them to your pond is a good thing for a diverse food chain. It would be unlikely the scuds would take hold in an established pond without extensive cover and even then it would be a challenge. In a new pond without fish, you would have better luck.
If you were trying to grow larger RES, the fingernail clams would be an excellent food source. Cecil, do you know what type of parasites fingernail clams harbor? I had not heard of them as being a host to any fish parasites.
