if a three foot grouper can kill a six foot shark, then when larger it could take on Marlin. Marlin aint constantly at thoes speeds thoim sure a grouper could eat it, if it was in the right place at the right time
the grouper could always surprise attack tho, and I don't see those two him. there was a report of a three footer taking down a six foot white tip reef shark.. and wat if the marling is on a fishing rod and worn out, time to strike eh?