Originally Posted by tommaso889
i have decided that if any fish get too big i will ask the pet shop i purchased them from if i can swap them for smaller fish of an equal price
There is a problem with this approach that I'll try to explain.
According to information from biologists I have read to date, it is my understanding that fish continue to grow throughout their lives, unlike us for example [except I guess in girth
]. Keeping a potentially large fish in a small tank does often negatively affect its growth, but this is not a benign process resulting in the creation of a miniature version of a normal adult; rather it is known as stunting, and this has negative impacts on the fish's health. Internal problems may not manifest themselves for years, but they can lead to an early death for the fish. Immune system problems have frequently been traced to stress, and a fish that is built to grow but is prevented from doing so by the physical restriction of the tank with the accompanying poorer water qualtiy (in relation to the fish's needs) is bound to experience stress.
One of the obvious issues is poisoning from ammonia. It is known that even levels of ammonia that are well below toxic to a fish can hamper the fish's growth. Fish produce waste, and as I have written elsewhere no filter can remove the urine and liquefied solid waste, only a water change does this. The smaller the volume of water in relation to the fish--including their number and size as this affects the amount of waste entering the water continually--the more toxic it becomes within hours. Experiments carried out by knowledgeable individuals like Jack Whattley and David Boruchowitz have proven that it is the water quality more than the physical dimensions of smaller tanks that impact most on a potentially large fish.
Where this leads is that any fish with the potential to grow to a large size should only be housed in a tank that provides sufficient space and thus adequate water quality to allow what nature intends for the fish. The relatively fast growth rate of fish will be negatively impacted by inadequate housing long before the physical size of the fish might suggest larger quarters.