MAIN INDEX | Grass carp and habitat management |
Physical characteristics |
Grass carp in Florida |
Grass carp diet | Caveats | How many is too many? |
How to remove grass carp | Training grass carp |
Useful links |
Chinese grass carp are herbivorous (plant eating) fish that have been purposely introduced into many Florida lakes and ponds as a way of controlling aggressive aquatic weed growth. For many, grass carp and aquatic weeds seem like a match made in heaven: the fish are relatively inexpensive and they have a ravenous appetite for problem plants - especially hydrilla. No lumbering harvesters needed, no expensive chemicals; just stock the lake with a few dozen hungry carp and let them do their thing. Right?
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To Be Or Not To Be - Sterile Normally, grass carp require free-flowing river systems to spawn and produce eggs, so it is believed they don't pose much of a threat to lake systems. However, grass carp have been known to escape from stocked lakes or ponds into neighboring waterbodies; this may explain the presence of numerous breeding populations of grass carp in a number of states along the Mississippi River. In Florida, three adult fish, including one gravid female, have been captured in the Suwannee River. When grass carp are able to produce viable eggs, they are said to be "diploid" - they have the right number of chromosomes. But Florida law says that grass carp used for weed control must be sterile and unable to produce viable eggs. They must be "triploid".
"Triploid" Chinese grass carp are hatchery-raised fish that have been sterilized by “shocking” fertilized eggs with drastic changes in temperature or hydrostatic pressure; the result is an extra chromosome in the egg, leaving the fish effectively sterile and unable to produce viable eggs. This technique is used to try to eliminate any possibility of their freely reproducing in Florida waters.
Sterilization techniques are not 100% effective. One study showed that milt from some triploid males was used to successfully fertilize eggs from normal diploid female grass carp. Other studies have shown that triploid carp are able to produce viable eggs and sperm, albeit in very low numbers. Because of these anomolies, some scientists suggest that every single fish be genetically tested by blood or tissue analysis, before stocking them into a lake. A number of states in the U.S. have taken a more drastic approach and have banned grass carp altogether — both diploid and triploid grass carp are illegal in some states.
Triploid grass carp cost between $6 and $18 each and are usually stocked at three to ten fish per acre, resulting in aquatic plant control for as low as $15 per acre. This is considerably less than herbicides, which cost between $100 and $500 per acre. Mechanical control is even more expensive, often costing more than twice as much as herbicide treatments. In Florida, only triploid grass carp are allowed and a permit is ALWAYS required, even when stocking “private” waters. Permits may be obtained by contacting the Florida Fish and Wildlife Conservation Commission (FFWCC). Be sure to read the rest of this webpage for the pros and cons of using grass carp for aquatic plant control.
http://floridafisheries.com/permits/carp.html (general information)
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grass carp |
Keep Reading
Anyone
considering stocking grass carp into their lake or pond should peruse these
pages and related links before taking the "plunge;" while they are an
effective and affordable solution for many lakes, grass carp are not a panacea
for all plant infestations. Under certain circumstances, they can create their
own set of problems.
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grass carp |
Grass Carp in Florida
Chinese grass carp were originally imported
and stocked into Florida lakes in 1972 as part of an experimental effort to
control hydrilla. When stocked in high enough numbers,
the fish
proved to be extremely effective plant harvesters.
However, lake managers and biologists were also in for a few surprises: when attempts were made to remove the fish from the lake, they were amazed at the the carp's uncanny ability to outsmart virtually every type of fishing technique. Nets, hook-and-line, electro-shocking, even poison baits were minimally successful, especially after the first application. It soon became apparent that once released, grass carp were nearly impossible to remove. As of 2005, there are still no easy ways to remove grass carp from a stocked lake.
| Favorite plants of the grass carp
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| Least favorite plants of the grass carp
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Aside from being hard to catch, there are several more caveats to be aware of:
It works like this: when open-water algae (phytoplankton) no longer have
to compete with larger plants for nutrients, the algae soon become the dominant plants within the system.
Within weeks
or months, the clarity of the water can be significantly reduced as algae increase in number and are suspended
in the
water column, turning the water an intense green color or even forming a surface scum on top of the water.
Another consideration: Aquatic plants serve as stabilizers for bottom sediments and once removed, the potential
is
increased for sediments to become re-suspended into the water column, further decreasing clarity.
Chinese grass carp are not always selective about the plants they eat; they may start with their favorite plants, but once
those are consumed, grass carp have been known to eat every single plant in a waterbody — including submersed, emersed,
and floating plants. They’ve even been seen wriggling out of the water to eat grasses along the shoreline!
If grass carp are stocked in high enough numbers, there is the potential for a lake
to change from a clear-water plant-dominated
system to a murky algae-dominated system. This dynamic is sometimes overlooked and as a result there have
been a number of
unhappy lakefront homeowners over the years.
At low stocking rates (two to five fish per acre), it can take six months to a
year before plants begin to noticeably decrease in
abundance. And because grass carp generally eat plants starting with the roots (instead of the extremities
such as leaves
and flowers), their effectiveness is sometimes underestimated. When this happens, people have been known
to stock
more fish into the lake. In some instances, this has resulted in “over-stocking” and the unintended
removal of every single plant — an unhealthy state of affairs for most lakes.
Grass carp can live for 10 years or more. The older they are, the larger they become and the more food they will consume.
If high numbers of fish are stocked, this can translate into the loss of a tremendous amount of plant biomass within a lake.
For more information, view the following paper: The Water Quality and Fishery of Lake Baldwin, Fl:
4 Years after Macrophyte Removal by Grass Carp.
The loss of too many plants may also have a negative effect on native fish populations that rely on plants for food, shelter
and spawning habitat. This situation can result in conflict between anglers who want some vegetation in a lake and other
users who think of plants as a nuisance or navigational problem.
In addition to the potential problems listed above, it is
thought that grass carp imported from China, have been the source of an Asian tapeworm that has infected the native
(and endangered) fish, the woundfin Plagopterus argentissimus.
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grass carp |
An ongoing debate: how many is too many?
Ever since Chinese grass carp were
introduced to Florida waters, efforts have been made to develop a formula to
accurately predict the appropriate number of grass carp for stocking
purposes, based on lake size and plant coverage. The ideal goal is to stock just
enough fish so that aquatic weed consumption slightly exceeds aquatic weed growth.
According to the Florida Fish and Wildlife Conservation Commission, this can be achieved with approximately two to five fish per acre of submersed vegetation. However, according to another group of lake experts, this formula has produced mixed results. In fact, when using Florida LAKEWATCH data, one study shows a breaking point for the use of grass carp in aquatic plant control.* If stocked in high numbers (greater than 10-12 fish per acre of aquatic vegetation), grass carp were efficient at eating virtually every submersed plant in a lake. In some instances, they ignored a few less palatable plant species (water lilies, bacopa and water hyacinths), but the rest of the plants were effectively gone.
(* Sandra G. Hanlon, et. al. 2000. Journal of Aquatic Plant Management. Evaluation of macrophyte control in 38 Florida lakes using triploid grass carp. 38: 48-54.)When stocked in lower numbers (less than 10-12 carp per acre of vegetation), the growth rate of the plants was often greater than the consumption rates of the fish. The bottom line: very little plant control was achieved.
According to Florida LAKEWATCH's Mark Hoyer, this "all or nothing" situation isn't always a bad thing. If the goal is to completely control the growth of nuisance plants in a lake, grass carp provide an economical long-term solution without the use of herbicides. Also, grass carp are particularly useful in small urban lakes, where submersed vegetation is not as imperative for fish habitat. http://edis.ifas.ufl.edu/AG008>
For additional information, FFWCC Aquatic Plant Management Biologists can be reached at
352.357.6631 (Eustis)
941.648.3202 (Lakeland)
How to remove grass carp
Other baits recommended by the FWC in their grass carp publication:
traditional bread balls, dog food, corn, or even live worms.
Training grass carp
Dan Willis led the way with his master's degree thesis Training Grass Carp to Respond to Sound
as a Fish Removal Technique (Willis et. al., 2000). Data from his study suggest that it is possible to train grass
carp to respond to low frequency sounds, which, in turn, means that it may be possible to use the sounds to attract the
fish to a corral-type location or into large cages where they can then be trapped and removed. Ideally, this new technique
would make it possible to move the fish from one waterbody to another, after they've fulfilled their intended plant-eating
duties.
Willis' work went a long way in documenting grass carp's response times to sound and in establishing some of the more
effective frequencies. It was also determined that grass carp responded well to recordings of their own feeding sounds. In his
conclusion, Willis notes that it is still unknown just how long grass carp might be able to retain this conditioned
behavior and suggests that further study is needed. (Note: If carp can only retain this conditioning for a short period of
time, higher stocking densities might be needed. However, if they retain the conditioned behavior for a long time, lower
numbers of fish could be used. This, of course, translates into a more economic solution to plant removal.)
A few years later, UF/IFAS grad student Mike Duncan continued to build on this research for his
master's thesis (Duncan, 2002). He tested the feasibility of releasing grass
carp into a pond, training them to respond to the sound/food reinforcement, and then trapping them for removal. (Willis'
research was based on how the fish responded in large tanks.) Although the study was not replicated, his efforts showed
promising results.
Duncan established that when grass carp are stocked in a pond with plants, they still
feed on man-made pellets and are indeed trainable in a natural environment (versus tanks). He was also successful at
training and attracting the fish with sound and then trapping a good number of them. Subsequent trapping attempts in the
same area produced fewer fish. However, it was suggested that some of the fish escaped through a small opening in the
trapping device, as many were seen in the herding area even though they didn't make it into the trap.
Both studies are a step in the right direction for those who want a low-cost solution for aquatic plant control without
having to endure the long-term presence of hungry grass carp in their lake.
Folks should do a little homework when
considering grass carp as a possible solution to plant infestations. For more
information on the pros and cons of stocking grass carp, be sure to visit this FWC
website: http://www.floridaconservation.org/fishing/updates/triploid.html
Other important FWC links:
Links to relevant EDIS grass carp publications:
Dan Willis' published paper: Training Grass Carp to Respond to Sound for Potential Lake
Management Uses (Daniel J. Willis, Mark V. Hoyer, Daniel E. Canfield, Jr., and William Lindberg)
This page was compiled by Amy Richard with assistance from Alison Moss. This page is maintained by Alison Moss.
Vic Ramey is the editor.
DEP review is by Jeff Schardt and Judy Ludlow.
This project is a collaboration of
Grass carp on hook and line
When faced with hundreds of unwanted grass carp in Lake McMeekin back
in 1990, one individual took it upon himself to try and remove them one at a
time, using hook and line. He started each fishing session by tossing soybean
chum out into the water just off his dock. He then used molded dough balls made
from Hungry Jack biscuit mix (uncooked). Using this technique, the angler and
his neighbors reportedly caught more than 600 grass carp! Of course, before he
wet the first hook, he contacted the Florida Fish and Wildlife Conservation
Commission and then continued his plan with their blessing.
For more about Lake McMeekin's overdose of grass carp, click here for a pdf file.
Some researchers are investigating the possibility of training grass carp
to respond to underwater sound frequencies, so they can be herded into a smaller
area, captured and removed from a lake or pond after they've fulfilled their plant harvesting duties.
Two studies conducted at the UF/IFAS Department of Fisheries and Aquatic Sciences (since 1997) suggest
there is hope for removing grass carp from small lakes or ponds without having to resort to more drastic removal methods
described earlier.
Triploid Grass Carp Permit
Triploid Grass Carp Applications and Amendments
Grass Carp: A Fish for Biological Management of Hydrilla and Other Aquatic Weeds in Florida
Weed Control in Florida Ponds
Fish Containment Barriers
General Principles of Weed Management
Data is from the APIRS database.
the Center for Aquatic and
Invasive Plants, University of Florida,
and the Bureau of Invasive Plant
Management, Florida Department of Environmental Protection
CAIP-WEBSITE@ufl.edu
Copyright 2005 University of Florida
