They can quickly take over from native fish in rivers.
Other species of native fish have also been affected by the low water levels.
Recently the government released native fish to improve the population.
All other native fish are no longer extant in the lake.
Scientists are worried that this will harm the numbers of native fish.
Although there's a lot of native fish, or something like fish.
Let Uhura eat the native fish if she wanted to.
The other native fish will be affected to a lesser extent.
The effects of this on native fish and bird species are still not fully understood.
It is not clear that the few problems you indicate for native fish result from stocking.