I know I'm just getting into the hobby, but I have an odd question based on my boyfriend's experience today. He has slightly more experience with fish and is establishing a 30 gallon marine tank while I play with fresh water. We were at King Ed's yesterday and the asian gentleman sold him a fox face rabbit fish (really cute btw) and we got him home and put him in. I went online afterwards and discovered that the tank was too small and that it is actually quite poisonous. We took it back today and the gentleman told us that it would grow to the size of it's environment. When we questioned him on it, he walked away. My question is: Is it true that a fish like this will stop growing once it reaches the capacity of it's environment?