Is it true that goldfish (or other captive fish) grow in proportion to the size of the tank they live in? I have a small goldfish in a tank at home but have seen much larger goldfish in ponds and believed they were a different species. But a friend insists they are the same, with the size difference being caused only by the volume of the body of water in which they live. Is my friend right? And if so why?
Barry Dwyer, Truro, Cornwall, UK