The atmosphere created in this poem is one that is frankly very menacing as the picture of the pike is built up, particularly focusing on the way that it is such a ruthless predator and so merciless. Note, for example, how the atmosphere is built up of the pike as a killer in the very first stanza:
Pike, three inches long, perfect
Pike in all parts, green tigering the gold.
Killers from the egg: the malevolent aged grin.
They dance on the surface among the flies.
Hughes uses a number of literary techniques in order to help him develop the atmosphere of fear that is conjured up through the pike. The alliteration of the "p" sound, delayed through enjambment, and then intermittently repeated gives a menacing, eerie feel, and the reference to the colouring of the pike, with "green tigering the gold" compares the pike to a tiger, which is of course another carniverous beast that is feared by animals and humans alike. Pikes are "killers from the egg" and bear a "malevolent aged grin," and are shown to "dance" as they are so agile and fluid. From the very beginning of this poem, Hughes paints a picture of pikes that shows them to be relentless killers. This picture is one that becomes more menacing as the poem goes on, with finally the last stanza building up a picture that is terrifying as the speaker imagines the pike watching him as he goes fishing as if he were the pike's prey:
Owls hushing the floating woods
Frail on my ear against the dream
Darkness beneath night's darkness had freed,
That rose slowly toward me, watching.
The silence of the surroundings combined with the image of the pike slowly rising to meet the speaker, watching him all the time, is chilling and terrifying in the atmosphere it creates.