Even if the fact that fish will only grow as much as their environment allows them was true, putting a clown trigger or a tanq in a 50 g tank would definitely not be ok... From what I read how much and how fast a fish will grow depends on the types of food it receives and not how big the tank is. You must realize that there are proccessed foods available today is such variety that a fish in an aquarium will probably get all the vitamins, proteins fats, etc it needs to grow. In addition, these fish are caught in the wild, so unless you get a midget monster of nature which is not fed properly, it will probably get close to its normal size. There are fish that outgrow the tanks they are placed in, so suggestions you will get in this forum, or by various authors refer to minimum tank requirements.
Since you are new to the board, you will see that it is really helpful and the people are there to answer and suggest solutions to problems readily. I had a tank set up for 3-4 years, but when I found this forum I really got answers to questions, solutions to problems, and suggestions for reading (really important), that the lfs people did not offer or know.
I have recently read that a damsel will defend in the wild a territory equall to several square meters, so you can understand the stress that a confined environment will put on a larger species...
Finally as with people, fishes's immune system weakens if they are stressed (aggressive tank mates, poor water conditions, inadequate hidding places, etc) with all the consequences that this implies....
PS. I had a clown trigger in my 90 when i had it in the States, and I eventually had to give him away cause he outgrew my tank. So I am speaking from bad experience.(The lfs owner never told me that this will happen when he sold me the fish, and unfortunately i was not aware of the forum, and had not read as many books as should have)
