Use there latin name Hydrolicus scomberoides. As FR+ said they aren't really the easiest to keep. Very prone to ick andother disease. As for randomly dyeing off at a certain size i think the problem is lack of proper maintenance. It's like goldfish. They live 20 years and get 14" but misteriously none of them grow that way in captivity. Let me break it down for you, go with a monster fish that you can suit now because that 600g is gonna be a few paychecks down the road.