In a nutshell, ... Reds come into different classes because they live some of their life in the bays and the rest of it in the Gulf of Mexico after they reach their maturity.
Bay reds are commonly referred to as either:
1) rat red under 20" which is undersized to take home 2) slot red between the legal 20" - 28" which is the legal size to take home, or any redfish tag over 28" you may possess
If you catch a red over 30" in the bays in 2' or so of water it's a real thrill and can provide a site to behold ... they'll roll and create their own wake !!!
Surf Reds are commonly called Bull Reds because of their size and maturity.
Reds spawn in the surf by lining up along the beach of the GOM and the bull reds will line up parallel with the beach and "call the female redfish in" which they do by croaking real loud. Northerns are good spawning conditions for redfish in the surf.