Fish do not stop growing just because a tank is small.
But in many cases they do stop growing in small tanks, because it is very hard to keep high quality water without massive daily water changes, so they become stunted as water becomes too high in nitrate and other growth inhibiting, stress producing compounds.
But in many cases they do stop growing in small tanks, because it is very hard to keep high quality water without massive daily water changes, so they become stunted as water becomes too high in nitrate and other growth inhibiting, stress producing compounds.