Pond Boss Forums AQUATIC VEGETATION Controlling unwanted plants Sterile carp, duckweed, ...and northern pike

I help manage a 3 acre community pond in Connecticut. Spring fed, max depth 8ft, with an overflow weir to control water level. Last time we stocked the pond with triploid grass carp was over 15 years ago and I haven't seen them in a couple of years. Duckweed is starting to cover the pond this past summer. I'm inclined to buy some more triploid grass carp to help manage the duckweed, but, a bunch of idiot neighbors admitted to adding northern pike into the pond a few years back. We've seen them and caught some and they're huge (24"+ long). I understand they are voracious eaters and are considered an invasive species. If I add triploid carp to manage the duckweed, I fear I'll only be feeding the pike. Any suggestions?

Two of your solutions are BIG grass carp or lots of SMALL grass carp.

If you put in large enough TGC, then the pike can't eat them. However, I don't know how large you can buy at your fish supplier. (And larger fish typically get exponentially more expensive.)

You could also put in lots of small grass carp. At the start, they will be so small that a 24"+ pike would not consider them a worthy meal. However, if enough survive to adulthood, they will eventually eat up all of your duckweed and other plants and then keep your community pond muddy as they stir up the bottom looking for their next meal. You then have a grass carp problem instead of a duckweed problem.

Best solution would be a buddy in the area that needs to get rid of some big mature TGC from their pond. Help them catch/seine a few, and move them over to your pond.

Another option is herbicides to control or reduce your duckweed. If you can reduce the area of duckweed, then perhaps your existing carp can keep up with the remainder. (I suspect your old TGC are still in there unless you had something like a big winter fish kill.)

What is the main use of your community pond? If you add that info some of the experts may be able to give you some better alternatives.

Good luck on your pond management!

P.S. Are the pike reproducing in your pond? If it is only the original "bucket stocked" pike, perhaps work on fishing those out and then you may be able to get by with just the purchase of some more TGC. I suspect you could find some eager volunteers to help you catch large pike!

Be aware that many people believe that once Grass Carp get larger, they become less effective in eating vegetation. If we assume that to be true, you are really wanting young Grass Carp. However, if you would have to stock more GC to buffer against some predation by the Northern Pike, you could be in a situation where you have more survival of Grass Carp than you want if not as many succumb to the Pike.

In my experience grass carp as they get old they still continue to eat vegetation however since the big old GC are not growing as much weight each year as young 12"-24" GC they are not eating as much vegetation daily (annually maintenance diet) as those younger fish.

In the fall many fish farms sell the GC that they used to clean plants out of their ponds. These GC an be 14"-20" long way too big for 28" pike to eat.

Thanks Bill, I did not know that little tidbit.

I suspect the OP needs to call the fish farms directly to check, since that is probably not the type of info that is going to be on the "Sales" page of their website.