There's a sticky thread on P legality. However, here's the Prohibited Species list for FL:
FLORIDA - Prohibited Fishes and Aquatic Fauna
To protect and conserve Florida's natural aquatic resources and help ensure public safety, the Florida Fish and Wildlife Conservation Commission (FWC) prohibits (see list above) or restricts (see Restricted fishes) certain non-native fishes and aquatic fauna. Moreover, no person shall allow or permit any freshwater aquatic organism not native to the state to remain in the waters of any pond which is not maintained or operated for the production of such non-native species.
The FWC uses well-defined criteria to determine where a species should appear on the list. The most current list is available by checking the statutes (See 68A-23.008). Species that were included on the list as of July 2003 are described on this page. In general, prohibited non-native aquatic species, listed in red in the link box above, may not be imported, sold, possessed or transported in Florida. Very limited exceptions are made by permit for viewing at large public aquaria or for research, provided Commission-approved maximum security requirements are met. No exceptions are made for certain prohibited species, such as piranha. Research permits for prohibited aquatic species are also very stringent.
AFRICAN ELECTRIC CATFISH - Family: Malapteruridae (currently 1 genus and 2 species, of which Malapterus electricus is best known)
AFRICAN TIGERFISH - (Hydrocynus spp.)
AIRBREATHING CATFISH - Family Clariidae
PARASITIC CATFISH - Family Trichomycteridae (including Vandellia cirrhosa, Pygidium itatiayae)
ELECTRIC EEL - Family Electrophoridae (including Electrophorus electricus)
LAMPREYS - Family Petromyzonidae (including Petromyzon marinus)
PIRANHAS - Subfamily Serrasalminae (including Serrasalmus spp., Pygocentrus spp., Pygopristis spp., Rooseveltiella spp.)
SNAKEHEADS - Family Channidae (Channa spp.)
PROHIBITED TILAPIA - (Sarotherodon spp., Oreochromis spp., Tilapia spp.)
TRAHIRAS or SOUTH AMERICAN TIGERFISHES - Family Erythrinidae (including Hoplias spp., and Erythrinis spp.)
AIRSAC CATFISHES - Family Heteropneustidae (including Heteropneustes fossilis, H. kemratensis and H. microps)
GREEN SUNFISH - (Lepomis cyanellus)
AUSTRALIAN CRAYFISH - (Cherax spp., except for Cherax quardicarinatus in tank culture)
ZEBRA MUSSELS - (Dreissena polymorpha)
MITTEN CRAB - (Eriocheir)
There is also a Florida Restricted Species List. Check your state's .gov sites.