Gundigest - Here in central Missouri, the average silver that jumps in the boat or we get in our large mesh nets is about 12 or 13 pounds. The average bighead is a bit smaller than that. The biggest silver I've seen was 27 pounds and there have been darn few of them yet over 17 pounds - which leads me to distrust the many stories of size; every person who gets hit by one of these things says it was at least 20 pounds. But a 12 pounder can do a lot of damage if it hits you or your rod rack at 20 or 30 mph or more. The biggest bighead I've seen was about 48 pounds. Bigheads have been here in Central Missouri longer than silvers, so the maximum size is bigger. We see bigger silvers every year. The worldwide records of both species top out at just about the triple digit mark.

Rick - These fish have not been able to reproduce in any meaningful way unless they have a very long river to do it in. Has to do with the requirements of the eggs and larvae. There are probably some reservoirs that have long enough rivers upstream, but most won't. That doesn't mean the adults won't do great in lakes or reservoirs if people put them there. The most likely way for that to happen is if they are transported by bait buckets. The young of the silver carp look very like shad, and both species are sometimes used as bait, both by people who know what they are doing and others who haven't a clue what the fish are. If you catch your own bait, use the bait in the same place you caught it. Do not transport bait caught from the wild. As far as the upper Mississippi goes, some fish will be able to make it through the dams. The first bighead has been caught from Lake Pepin, really a pool on the Mississippi River. But I don't know if the fish will ever reach high populations or not. The fact that grass carp, which have similar reproductive requirements, have not become a big factor in the upper miss gives me hope. Maybe the dams will make recruitment of young impossible in those stretches, just maybe. But efforts to keep the fish from getting past the dams are probably wise. I wouldn't want to rely on that hope, and even if reproduction is not possible in the upper Miss, then continual immigration of bigheads and/or silvers from the sizable population downstream would be almost as bad.