Norm - Once the preferred plants are all consumed by the grass carp and these fish are greater than 28" they will discover they prefer the flowers of the fragrent water lilies. You willnotice the flowers do not last as long as they once did. Each flower lasts about a day when amur have discovered them. Also the amur will consume many of the newly emerging tender shoots of the lilies in spring as the lilies send the new pads to the surface. Degree of lily foraging will be dependant of how many amur are present and amount of other available, palatable vegetation.
