Pond Boss Forums AQUATIC VEGETATION Balance of plants in the environment Grasscarp, not a fan but?

Very good advice so far from guys with practical experience. It is wise advice heed it. Here are some of my thoughts.
You have a good thought process about managing your pond plants of trying to maintain a good amount of submerged weeds for your needs and maintain some habitat. My suggestion is to allow the current plants to expand and then when they are about 15%-20% greater add one grass carp(GC) each year to try and maintain your desired amount of weeds.

Important points. Prevent over grazing and pond denuding of pond bottom.
Grass carp prefer the more delicate softer submerged plants such as most of those in the pondweed and naiad family (Potamogeton, Najas). GC will less aggressively eat other more fibrous submerged plants when preferred plants are lacking. When food is lacking, GC have been seen eating lawn grass clippings that have been blown into the pond. Filamentous algae (FA) is not a preferred food and normally is not very well controlled by grass carp.

Here is a general guideline to determine how many submerged weeds a grass carp will eat.
When water temperature is above 60F, the adult and actively growing GC are said to eat 2 to 3 times their body weight per day when preferred plants are present. GC can gain 5 to 10 lbs/year when they are actively growing for years 1 through 6, then as they become old, feeding activity gradually decreases causing less feeding and slower growth. Life expectancy is 12-20 years.
Non-preferred foods usually result in less plant pounds eaten per year.

Many stocking recommendations suggest that after 5 to 6 years a second stocking is recommended at the rate of 75% of the original number stocked to compensate for the original stocked fish eating fewer plants. Proceed cautiously. Number of GC to stock depends a lot on how much of the pond bottom and surface are covered by weed growth. Missouri Conservation Dept. suggests that fewer GC are needed per acre (1-10/ac) when narrow leaf pond weeds of naiads, bushy pondweed, elodea, pondweeds and Chara are prevalent. Moderate rate is 4 to 6/ac. When ponds are dominated by coarse leaf plants such as water lily types, water milfoil, coontail, eel grass, parrot feather then 10 to 24 GC/ac are often suggested with 10 to 15 being a low-moderate rate. I also suggest you proceed slowly and start with lower numbers and as the fish are 2 to 4 years old you can add some more GC grazers depending on how many weeds are still present in mid to late summer.
I think your goal is to get 75% to 80% plant reduction to always leave 10-25% weed growth as good fish habitat and competition to filamentous algae. In Georgia, grass carp can grow to 29”(20lb) in 2 years. Wow!
I have calculated how many pounds of preferred plants grass carp will eat each year for Ohio climate. I used an average amount of 2.5 times their body weight when water temperature is 66F to 90F (OH this was 141 days). Standard amount is estimated to be 2 to 3 times body weight per day. When water temperatures are 50-65F (OH this was 73days), I used one body weight consumed per day.

Notice below as the fish grow, they eat a lot more plant pounds per year! This is why one should allow the GC to get some size before adding more fish grazers.

FishLgn Fish Wt Total Lb Plants/Yr One Fish Consumption
10-12" ====0.7lb ====297lb
16” ======3 lb ====1,276
26” ======10lb ====4,255
30" ======16lb ====6,808
33” ======21lb ====8,935
36"-38” ===36lb ===15,318

To adjust the amount of plants eaten for your area use the plant growing season days (number of days) of your pond location as your plant consumption guide.