Zach Eastlick of Hatfield, Wis., was carp fishing with a bow and arrow Saturday on the Mississippi River near Trempealeau, Wis., -- south of Winona -- when he arrowed this 21-pound grass carp."They knew they had something unusual because they fight like crazy,'' said Fred Christen of Osseo, Wis., who sponsored the boat Eastlick was using. "That's a good-sized fish.''Grass carp, an invasive species, occasionally have been found in the Mississippi for more than a dozen years, usually in the nets of commercial fishermen. One was caught in the St. Croix River in 2006."We haven't seen the population explosions (as other invasive carp have exhibited),'' said Tim Schlagenhaft, DNR Mississippi River coordinator. "They are vegetation eaters.''Grass carp, which can grow up to 70 pounds, are native to southeastern Russia and northwestern China and were brought to the southern U.S. in the 1960s to control aquatic plants in reservoirs and aquaculture farms.