As far as what crawdads eat, I'd say almost anything...live, dead, plant, animal, eggs, young, etc. I have not found a submerged plant that they won't eat. They seem to leave my Pickerel Weed, Arrowhead, and Water Canna alone, but they are pretty tough and emergents at that. They love American Pond Weed & Water Primrose, and do considerable damage to water lilies.
Brushy Pondweed should make a good meal for them given that there is not anything else in abundance that the craws would prefer. I find that the craws tend to chew the bases off of the submerged plants more so than eat the whole plant. In some cases this kills the plant, but in others it could promote more growth if the plant can grow from the cuttings.
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