they need xl tanks & good water quality & good diet- that tank is way too small if the tank is 1.5ft & the fish is 1.5ft it's too cramped they need at least 3" space so they can move easily .
Me and my mate just cut it and it seems to be already growing back can see about 1mm of new gill growing already and he has already got a 2.3 x 80 x 80 tank ordered which will be ready in about a month or two and the fish was from Le aquatics in lansvale they have some nice and exotic fish there