They are not crap! When I catch a carp, I take it home and dig a hole in my garden and bury it. They make great fertilizer.
I hear they eat a lot of turds that don't fully decompose in the sewage treatment plants and is transfered to our creeks and rivers. These turds are ingested in the little fishy bodies and distributed throughout their body for nourishment and growth. So I guess their bodies are made up of digested poop. Thus, fertilizer that you buy is poop, usually from cattle, so there ya go. Free poop.
There's a saying, "I'm goin to go take a crap." Which usually means, that.... Ah, never mind, I think you know. So I guess I stand to be corrected. Carp are CRAP!
Just my 2 cents...