Triploid Grass Carp
Triploid grass carp (Ctenopharyngodon idella) are an excellent biological control for many submergent plant species. They are particularly effective in controlling Hydrilla verticilatta.
Triploidy refers to the presence of an additional set of chromosomes in the cell nucleus. This condition is induced by manipulating the fertilized eggs of normal (diploid) broodfish. A variety of methods are used, including hydrostatic pressure, heat and cold shock. Since these methods are generally only partially successful, the progeny produced by these methods are then checked for sterility by performing blood tests on each individual fish.
Major advantages in using grass carp for weed control are:
Contrary to popular opinion, grass carp do not increase the nutrient levels in lakes. While it is true that algae blooms may occur after grass carp have significantly reduced the plant biomass in a water body, it must be remembered that the only nutrients added to the system by grass carp are those contained within the flesh of the fish itself. The algae blooms are indicative of a nutrient laden system; the removal of higher plants simply causes the redirection of nutrients into planktonic algae. It is unfair to compare a formerly weed-laden lake with pristine wilderness; rather, one should look at the water body before and after the introduction of grass carp, keeping in mind that the nutrients were the initial cause of the weed problem.
Also, grass carp do not feed on the young of other fish. In fact, grass carp are used in our fingerling production ponds to increase the yield of small fish. In this situation, grass carp are stocked at extremely high rates because we desire algae and zooplankton blooms. Since the production of juveniles would decrease if grass carp were predators, it should be obvious that such is not the case.
We believe in an integrated approach to aquatic weed control and we use herbicides judiciously and regularly as required. The key to aquatic weed control is to address the problem when it is a small one.
Florida residents may apply online to the Florida Fish and Wildlife Conservation Commission for a permit to possess and stock triploid grass carp at the FWC's Triploid Grass Carp Permit link.
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