It is impossible to know because Koi ponds are not registered so how would you know if someone has one in their back yard?
If you are asking how many eggs (ova) a Kio carp releases when spawning then the answer is many thousands.
700 US gallons = 2,649.78825 liters
Note: 4 Quarts = 1 Gallon 700 x 4 = ? Answer: 2800 Quarts