Really here is how I see it. The arapaima is more dangerous because you have a better chance to get attacked by them when they jump. the alligator gar is dangerous when you have it in your hands because it has a better chance to bite you. the mekong catfish probably wont attack you. the wels have had "reported" attacks,probably because of their nest being invaded while swimming. the goonch has had reported attacks and it could make sense too because of the funeral pyres. i think the most dangerous is the arapaima but the big catfish i would watch out for!