As a Freshwater Frog & Fish Dealer and a FWC Authorized Triploid Grass Carp Supplier, I get a lot of questions about grass carp. One of the most common misconceptions is that grass carp are an effective filamentous algae control. Believe it or not, the grass carp can be picky eaters with a preferred diet. While grass carp may occasionally eat filamentous algae, its often only as a last resort.
What do Grass Carp eat?
So we’ve established that Grass Carp for filamentous algae control isn’t a viable option…. So what do the Grass Carp eat? The University of Florida has published a chart showing the Grass Carp’s preferred diet.
Grass Carp Preferred Diet: Top 10
- Hydrilla
- Chara
- Southern Naiad
- Brazilian Elodea
- Watermeal
- Duckweed
- Azolla
- Pondweeds (Potamogeton spp.)
- Coontail
- Torpedograss
Source: University of Florida, IFAS Extension: https://edis.ifas.ufl.edu/fa043
While the Top 10 are summarized above, some of the other common aquatic weeds which rise to nuisance levels that the grass carp feed on are #15 Eelgrass (Vallisneria), and #20 Spatterdock or Cow Lily.
How many Grass Carp should I stock in my pond?
This question can have a complicated answer, but the first question to ask is “What is the pond used for?”
Stormwater ponds need capacity and overly abundant aquatic vegetation can have a big impact on a stormwater ponds function. For stormwater ponds, we recommend an initial stocking of 10 fish/acre. After the first growing season past a stocking, the rate can be revisited for effectiveness and moved as high as 20 fish/acre. Stormwater pond owners should also account for a population decline of up to approximately 20% per year due to predation and natural decline. This means every 5-years a restocking should be planned.
Owners of recreational ponds, or those managed as a fishery, need to consider that once stocked, grass carp are difficult to remove. The fish act as underwater lawnmowers, eating 24/7/365 and can completely wipe out submersed vegetation within a pond. This can have a detrimental effect on the use of the waterway as a fishery, as the grass carp will eat the submersed vegetation necessary for a healthy fishery. Additionally, waterfowl forage on and in the submersed vegetation, so fewer waterfowl will be attracted to a pond with less submersed vegetation. Given this, if a recreational pond owner wants to use grass carp in their management plan, a lower stocking rate of 3 to 5 fish/acre is generally suitable.
A few last words…
In Florida, Grass Carp are permitted and controlled by the FWC. At the end of the day, the FWC Biologist who issues your permit has the final say in how many fish will be permitted. It is important to have a discussion with the FWC Biologist and your lake management provider so that the appropriate stocking rate can be approved.
And lastly, I often get calls from pond owners who are in dire straights. While the grass carp and other biological controls are effective tools in a pond managers tool box, they rarely achieve “renovation” goals and are best often suited for “maintenance” goals. Grass carp should be utilized in conjunction with a full-scale Management Plan, utilizing all the resources available to the pond owner.
FWC Permit Information: https://myfwc.com/wildlifehabitats/habitat/invasive-plants/grass-carp/
