We have this same problem in Thailand. It's the breeding between Giant Grouper(Tamagai) and brown-marbled grouper called Dragon's Pearl Grouper (translated from Thai). The farmed fishes leaked through the vast ocean around 10 yrs ago, has been found occasionally, without any eggs or shirago sacks inside but lots of visceral fat. the biggest one I've got weighed 19.4 kg. I don't think It's healthy for the ocean environment to have too much of these carnivorous fishes, but we can't do anything bacause the government don't give a thing about fisheries unless they're endangered