Here is what the Florida Fish and Wildlife folks have to say:
Is culling allowed?--Answer: The rules are different in fresh water
and salt water. Culling has always been allowed in fresh water
provided that released fish are alive and that culling is done
immediately. The rationale in part is biological but in part
historical. Recreational fishing has been regulated for much longer in
fresh water than in salt water, partially because of perceived impacts
on the resource (some people used to think the oceans were too large
to be impacted by recreational fishing or management efforts). Culling
was allowed very early on in fresh water and became widely accepted as
a fresh water practice throughout the nation for both individual
anglers and tournament anglers when live wells became common. Wanton
waste rules continue to prohibit discarding dead fish to deliberately
replace them with a larger live one. Remember that fish that are
illegal to possess because of species, size or bag limits cannot be
kept, even if they died or are likely to die as a result of catching
them, consequently they must be released.