both different species. BATF grow significantly smaller compared to GATF. if i am not mistaken the largest GATFs in captivity reach 40'' ++ whereas brevis only reach around 20-24'' if kept properly.
fishtankphil
has or had one above 40'' before. think about it this way, mcdonalds and KFC both serve fries, but are different in taste and looks. BATF are much harder to find in the hobby as well compared to GATF.