Fish isn't my favorite...
Fish Bukket is an electronic/orchestral song about a cat who loves fish but cannot catch or keep them around. Without the fish, the cat feels consumed by a void. Ultimately, the cat realizes that despite being haunted by it, there is no reason to continue to be hurt by the void.
"Fish" aren't really fish here; they represent friends derived from the cliché "there are plenty of fish in the sea."