you can measure a fish with or without tails/fins, with them is called Total Length or TL, without them is called Standard Length or SL, scientific records do use SL most of the time though a lot of us don't so we can boast the sizes of our fish muahahahaha
anyway, there has been wild carp (same species as koi but without coloration) that was caught at almost 6 feet however most koi don't grow past 3 ft even in huge ponds, we can't count extremes and expect our fish to grow that large, we don't all grow into shaqs and yaos, what i was saying was: no way goldfish grow to 2 ft on average even in optimal conditions
Bruce is one huge oranda