Tilapia serve as a natural, biological control for most aquatic plant problems. Tilapia consume floating aquatic plants, such as duckweed watermeal (Lemna sp.), most "undesirable" submerged plants and most forms of algae.[14] In the United States and countries such as Thailand, Tilapia are becoming the plant control method of choice, reducing/eliminating the use of toxic chemicals and heavy metal-based algaecides.

Tilapia rarely compete with other "pond" fish for food. Instead, because tilapia consume plants and nutrients unused by other fish species and substantially reduce oxygen depleting detritus, adding tilapia often increases the population, size and health of other fish.

Arizona stocks tilapia in the canals that serve as the drinking water sources for the cities of Phoenix, Mesa and others. The fish help purify the water by consuming vegetation and detritus, greatly reducing purification costs.

Arkansas stocks many public ponds and lakes to help with vegetation control, as a robust forage species and for anglers. I found this here http://en.wikipedia.org/wiki/Tilapia Maybe the secret to catch them is to use something entierly different like some aquatic plant immitation? I cannot test this here because the water temperature is to low for them to survive.