I don't have the info in front of me, but I'm pretty sure low doses of rotenone can select for the gizzard shad. You might also check on the availability of a chemical called Fintrol. While working for the state, I watched one of our hatchery managers apply it at low doses in shad contaminated catfish grow-out ponds. He whacked the shad and the catfish were unharmed. I have no idea what the dosage was or even if Fintrol (spelling may be wrong) is still available, but the gizzard shad were less tolerant to it than other species. Because of this, the low dosage was used to select for and only kill the shad.
Some research on using these piscicides at low dosages to select for shad only might be worth it to you. I know its been done. I wish I had more technical info for you, but perhaps this limited info can point you in the right direction.
