What about other 1%

In the beginning, there were 200 × 0.99 = 198 blue fish in the aquarium out of 200.

After removing n blue fish from the aquarium, we will have (198 -n) blue fish out of (200 - n):

$\frac {198 - n}{200 - n} = 0.98$

$198 - n = 196 - 0.98n$

$2 = 0.02n$

$n = \boxed {100}$

Initially there were 198 blue fishes out of 200.

If we remove 100 blue fishes, then there remains 98 blue fishes out of 100 i.e 98%