Who has the power in "The Fish," the speaker or the fish? Well, it would immediately seem that the speaker does, because she is responsible for determining whether or not the fish will survive. However, as the poem progresses, we start to see evidence of the power the fish has over the speaker. It's not physical power; it's something we can't quite put our finger on that moves the speaker enough to contemplate the fish and finally set him free.
Neither the fish nor the speaker holds the power in this poem.