Can you keep a flathead catfish in Kansas?

No minimum size, five a day — same as Milford and Cheney, neither reservoir carries a flathead exception.

KDWP source page

What we left out on purpose

• Kansas's blanket rule — possession is three times the daily creel limit unless a water lists its own possession number — was applied to every statewide and named-water entry above. No individual water in this table stated a possession number that broke from the 3x rule.
• Milford and Cheney both carry dozens of further named-water rules across Kansas that are not modelled here — only the two reservoirs this site actually reports on (Milford Reservoir, Cheney Reservoir) got individual regions, the same restraint used for Colorado's Gold Medal waters and Louisiana's and Mississippi's named-water exceptions.
• Bullfrogs (8 per day, 24 in possession after day three of the season) are not a finfish and are not modelled here, consistent with every other state in this silo.