Pond Boss Forums MANAGING AN EXISTING POND Corrective stocking NC Blue Tilapia ?

FISH AS BIOLOGICAL CONTROL AGENTS FOR AQUATIC WEEDS
For submersed aquatic weeds, herbivorous (plant-eating) fish are an attractive alternative to herbicides and other temporary methods of weed management. This type of biological control often requires less labor, fewer treatments, and less expense than other methods, and it has good potential for long-term management of aquatic vegetation.


Occasionally, the blue tilapia (Tilapia aurea) has been used to control algae, and the redbelly tilapia (Tilapia zillii) has been used to control aquatic macrophytes (coarser vegetation) in North Carolina. Because tilapia are tropical species and cannot tolerate water temperatures below about 50deg.F, they are unable to survive normal winter temperatures and have limited use for weed control in North Carolina. Common carp (Cyprinus carpio) and several variants of this species (for example, Israeli carp) have also been used for weed control. In most situations, these fishes have not been very effective, as they are omnivorous (eat a variety of foods) rather than strictly herbivorous. In cases where they have been effective, most of the control has resulted from their habit of muddying the water while rooting in the pond bottom for food, rather than from the actual consumption of vegetation. The triploid sterile grass carp (Ctenopharyngodon idella)is the primary fish used for the biological control of aquatic vegetation in the United States.

Tilapia. The tilapia are tropical species that
can suppress growth of aquatic vegetation
(such as filamentous algae) when stocked at
high rates (300 per acre). Two species of
tilapia have been considered for weed control.
The blue tilapia (T. aurea) feeds entirely
on algae (both planktonic and filamentous)
but does not readily consume submersed macrophyte
vegetation. The redbelly tilapia (T.
zilli) feeds primarily on submersed macrophytes
rather than algae. However, both species
reproduce rapidly and consume both the
vegetation and the small animals living in the
vegetation that are important food sources
for desirable fish populations. Therefore, use
of the tilapia may have unwanted environmental
consequences. Tilapia cannot survive
normal winter water temperatures in North
Carolina, however. This is a benefit from an
environmental standpoint, but annual restocking
is necessary unless a warm water supply
(such as thermal spring or power plant cooling
reservoir) is available as a refuge in
which the fish can overwinter.
Fish also may be seined in the fall before
the onset of cold weather and either harvested
for food or maintained indoors for restocking
during the next growing season. The loss of
fish in the fall when water temperatures are
too cool for survival may require the removal
and burial of large numbers of dead fish at the
end of each season. Usually, they will be
consumed by bass or predatory birds before
they die.