I agree.. Your best off not keeping the fish with anything,unless the tank mate is actually larger than the gator gar.Even with that size tank mate,you could still readily have the gator gar attack it.
they wont kill each other unless one is much bigger than the other.
dont get one unless you have a giant tank,pond.
theres one in the pond with tons of other fish.
other fish will be eaten.
a pacu could work.
since they get so big so quickly.