All large aquatic plants need to be removed from the ponds. The tilapia are largely eating phytoplankton and zooplankton which are in turn encouraged (bloom) by adding organic and inorganic fertilizers to the pond. Phytoplankton get the nutrients they need from the water column but rooted aquatic plants can compete for that also and from nutrients in the pond bottom. They can then shade out the phytoplankton largely preventing it from growing at all. This makes the grow of the tilapia tiny in comparison to ponds without large aquatic weeds which the tilapia can't eat. Worst of all is that the shade from floating large aquatic plants such as pond lilies prevents oxygen production beneath them. Thus successful tilapia fish culture requires that all large aquatic weeds be removed from the ponds.