The biggest issue faced, is most all saltwater fish cannot tolerate cold water. In the ocean, the migrate north for the summer but when temps begin to fall they head back south. If confined to a pond, they cannot migrate back south and die. Bobby lives in FL, so his pond stays warm year round...
Some species have juveniles which are more tolerant of low or no salinities, but adults need salinities closer to oceanic water. This may be a biological thing, allowing smaller juveniles to ascend rivers where predators may not be quite so big and abundant while the adults don't need this as they are larger. Last weekend they were catching red drum in the Potomac River within view of the Washington and Jefferson Monuments. Salinity levels there are nearly pure freshwater.
