RE: Need help cooking and eating Grass Carp
Christine is right. Really big ones can be marginal eating. I recently cooked up a 50 pound black carp and it frankly was terrible, but I really like the fifteen pounders - they are just like grass carp. I have not tried a grass carp over 30 pounds, but that is about the size they get a bit weird. The flavor gets stronger, and the fascia between the myomeres becomes thick enough to notice. I have done the same thing with redfish - when they get huge like that, that fascia becomes noticeable, and it is not something you really want to notice.
Also - grass carp are not immune to picking up off-flavors that result from bluegreen algae blooms. Of course, catfish are famous for that too. You might notice a bluegreen bloom - some kinds form a thick layer of green near the surface, and your boat will sometimes leave a clear-water track through it. But not all kinds of bluegreens act that way. It can happen at any time of year. Not terribly common, but results in nasty fish sometimes.