How can I tell a grass carp from a native carp?

I'm curious, are there any clearly definable traits that distinguish a grass carp from other carp species?

Occassionally, I'll catch a carp in a local lake that was stocked with some grass carp a few years back. Not knowing one carp from another, my 1st inclantation is to thow the fish out (treat it as an unwanted trash fish) but I'd hate to eliminate a desired species so I usually return the carp to the water.

Thanks for the info.

The mouth of the common carp is more downturned with a bugle/sucker look. The grass carp's mouth sits more to the front of the head without a sucker apparatus. Seems like the grass carp is a little lighter in color generally, and is more torpedo shaped (elongated). There's other differences that could be addressed by forum member smarter than me. Such things as number of fin rays and tail shape, etc.

Grass Carp do not have barbels (whiskers) on the mouth. It's been about 35 years since I caught a German Carp, but I believe they have (four?) barbels at the sides of their mouths.

Alternatively, Grass Carp lips look just like The Incredible Mr. Limpet's.

Do a search on the net for pics and you will find not only some physical differences as states earlier, but these two species look as different as night and day.

Thanks guys.

In hindsight and with the helpful info you provided, I am now convinced that the carp I caught were in fact grass carp.

The water body was badly overgrown with alge and I was actually fishing it to see if I could get any good sized bluegills or redears out of it. No such luck: the only thing I caught was grass carp. I remember being suprised because I fished using worms, and I know there once was a sizable bluegill population in the lake.

The carp I caught were small, it will be interesting to see if next summer they have been able to grow in size and/or keep the alge and weeds at bay in this public lake.

I suspect that farm runoff has made this body of water (10-15 acres) so highly fertilized and silted so that no amount of grass carp intoduced by the DNR or some other source can keep the plant growth under control.

Has anyone else ever seen a lake that would not respond to the introduction of grass carp? This lake has been overgrown with alge and weeds for the last 10 years or so.

Thanks again for the info.

My lake was overgrown with coontail and Eurasian milfoil. No matter how many grass carp I introduced I could not make inroads into the vegetation. I killed it off with herbicide 2 years ago and have not had any regrowth. I am pretty sure this is due to the grass carp. I have maintained an almost perfect turbidity since killing the weeds (before, the water was very clear) no doubt courtesy of the released nutrients from the dead vegetation. Pond of 3.5 ac, added up to 60 grass carp in frustration.

Here is a close-up picture of a grasscarp. Their "intake-port" is considerably different from that of common carp or drum species.

Great picture! They aren't the prettiest fish in the lake.

Their mommas think they're pretty.

If you think they're ugly you should take a close look at a bighead carp.
robert B