The key theme of this poem is the ageless and unchanging violence of nature—something that cannot be tamed by human intervention and which is so elemental that the speaker's "hair [is] frozen" on his head at the recognition of it. The pike the speaker sees in his pond at night are "legendary," watchful; they are a "darkness beneath night's darkness," something "immense," whose power is palpable. It is very clear to the speaker, as he fishes in the wide pool which has endured so many years, that the power, the particular violence, of the pikes within is greater than his own power. There is an aspect to nature which is driven by violence and darkness and is beyond the capacity of humans to control.

This is indicated throughout the poem. The pike are "killers from the egg," born violent and born sure of their own enormity in their own world, too. Although they are only three inches long at birth, the speaker is sure that they are very conscious of their own "grandeur," such that they feel hundreds of feet long, confident of their own power. The violence of the pikes is emphasized, too, through such words as "jaws" and "clamp." The attempt by the speaker and, we must presume, his friends, to tame three pike ended in disaster: the result was that one of the pikes killed another, leaving only one of the three alive. The speaker has attempted to control the pikes and turn them into something humans can dominate, like a pet. But the violent nature of the pikes cannot be controlled. In the end, their elemental and ageless instincts win out, and they remain as they have always been, uncaring of human desires.