When harvesting fish, there are many guidelines to abide by set by the FWC. If you need an overview about size/limits/fish types, you can start here. The provided link allows you to start your search and can help prevent fines from harvesting the wrong size/limit of a fish.
There are some species within the Gulf of Mexico state waters (keep in mind, there is a difference in state and federal waters!) that do not have a season closure, such as: King and Spanish Mackerel, Snappers (except Red), Lionfish, Sheepshead, and more!
You may view the link here and it is even printable. This link, if you scroll down to the second page can actually link you to the size and bag limits of these fish for easy navigation. There are some prohibited species that you should investigate further before harvesting. There are different types of prohibited sharks, Groupers, Conchs, Eagle Rays, and Sturgeon, just to name a few.
These regulations are for Gulf of Mexico State Waters ONLY, do not abide by these regulations if you are in Federal Waters. You can find information at the link provided here. This phamplet does not contain ALL information needed for harvesting fish in the Federal Waters in the Gulf of Mexico. Make sure to follow all regulations set by the FWC in order to avoid fines.