There have been 5 bonafide confirmations of cougars in Louisiana. See the confirmation map here and click on the numbers in Louisiana for the information about each cougar verified:
http://www.cougarnet.org/confirmationsAs far as 'black panthers' are concerned, about the only chance that Louisiana has ever had a wild 'black' big cat at any time in the past was probably the melanistic (black) phase of the southern jaguar - which 'may' have been here in numbers before the 18th century. There has never ever been a 'black' cougar confirmed in the entire USA.
Any other actual 'black panther' sighted in Louisiana may have been an escaped black African leopard from a zoo (supposedly rumors have one escaped a small zoo at Chicot State Park at one time) or whenever the Carolina Panthers play the Saints in the Superdome.