line
George
I think there are a lot of variables to be considered when choosing your line.
When fishing from a boat or in open water 30 pound line combined with quality reels with a proper drag set will whip a very large catfish. I got a fairly nice flathead from bait set next to an underwater tree on a spinning rod loaded with 30#.
If you are fishing swift current or snag infested waters you may consider using heavier line. But there are circumstances where flatheads will not be caught even with the heaviest line.
Remember it is better to get a big cat on and lose him than to never hook one. The more you hook the better your odds of landing one.
When fishing you should prepare as best you can and then deal with each fish as they come. Every catfish trip is unique and will build a lifetime of memories to be savored forever.
Remember to release the trophy cats to spawn, grow, and fight again!
