Spoken by a fish in a tank, the poem sounds almost casual at first: "A fish's life isn't easy." But the list that follows is heavy. The fish can't close its eyes, can't stop swimming, can't shut out sounds it never wanted to hear. It doesn't sleep or dream, so there is no escape, not even into imagination.
The second stanza narrows the world further. A few strokes ahead, the fish will "kiss the cold reflection / of my own self." The glass turns the fish's only company into its own image, which feels chilly and lonely. Read more widely, the fish could stand for anyone stuck in a restless, watched, noisy life with nowhere to go.
The last line, "Thank you, Lord, for this glass cage...", is bitter and ironic. The speaker seems to be thanking God for a prison, and the trailing dots leave the tone hanging between resignation and quiet protest. The mood is weary, claustrophobic, and darkly humorous.