I would contest that what is left over from grass carp digestion process does not directly or indirectly encourage filamentous algae or macrophytic growth. We've seen grass carp enrourage planktonic algae growth, but that is exactly what we want for fish growth. Cellulose, being the major structural component of plant cell walls, is indigestible to all single-stomach animals, including fish. In addition, undigested cellulose, is not a readily available nutrient for direct uptake by plants. It must first degrade into basic nutrients.
I think that the efficiency of the grass carp digestion is interesting, and have read that they can grow to several hundred lbs in their native environment. They may be inefficient eaters, but most plant-eaters are inefficient. Consider the economic efficiency of grass carp in comparison with herbicides, labor, time, etc. The alternatives to grass carp may include chemicals and countless hours of mechanical removal which has to be repeated throughout the season and every year.
Grass carp are an integral part of some of our management programs. They help us to feel comfortable with fertilization programs where macrophytes already exist, and they improve the efficiency of fertilization programs.
I agree that grass carp can cause problems, but I also must insist that they are a valuable tool for pond and lake management when stocked responsibly.
