Can you keep a catfish in Mississippi?

No statewide creel limit and no minimum length. The rule is explicit: "There is no daily creel limit for any game and sport fish species not listed above." Individual state fishing lakes set their own limits.

MDWFP source page

What we left out on purpose

• Border waters follow an unusual rule that has no field in this schema: for black bass, bream, crappie and striped bass in waters touched by the state line, the limit is that of the adjacent state or Mississippi’s, whichever is greater. Anyone fishing the Mississippi River or Pickwick Lake needs both sets of rules.
• MDWFP’s own page links the April 2023 revision of the creel rule, while a May 2024 revision "with CHANGES" sits on the same server. Both were read; the statewide creel table is identical in the two, so nothing here depends on which is current. Anything beyond that table should be checked against the newer file.
• Mississippi sets freshwater length limits lake by lake rather than statewide — Arkabutla, Enid, Sardis, Grenada, Eagle Lake and others each have their own for crappie and bass. None of those waters is reported on by this site, so only the statewide creel figures are carried.
• Paddlefish is left out. Mississippi measures it from the front of the eye to the fork of the tail, a method this schema does not carry, and fish over 30 inches must be released.
• The reef species — snappers, groupers, amberjack, triggerfish — carry aggregate limits and federal seasons set by the Gulf of Mexico Fishery Management Council, which change within the year. Only size and bag are published here, not the season.
• Sturgeon of every species may not be taken or possessed in any Mississippi water. It is left out rather than listed as a zero.