For the first time, 200 fish were caught for marking, and 7 of the 490 fish caught for the second time were marked, so the ratio of the marked fish to the total surviving fish was 7: 490 = 200: X, and X= 14000 was obtained by solving the equation.

Survival rate = (number of surviving fish ÷ total number of cultured fish) ×100% = (14000 ÷ 20000 )×100% = 70%.

So the one-year survival rate of carp is 70%