Two lines are all it takes here, and they hold a surprising amount. The speaker pictures fish touching one another, a small, quiet contact in the water, and says it helps them understand "something of the night." The poem doesn't spell out what that something is, which is part of its pull.
The title, "Piscean," points to fish, and it may also hint at the zodiac sign Pisces, though the poem never confirms this. Either way, the focus stays on closeness. Fish moving through dark water, brushing against each other, seem to stand for the way night feels: hushed, intimate, a little mysterious. Night becomes less like an absence of light and more like a place where living things find each other.
The mood is calm and hushed, with a touch of wonder. The speaker sounds humble, admitting only to understanding "something," not everything. It reads like a moment of quiet insight, offered gently and left open for the reader to finish.