The poem's strange little scenario starts with a coin or banknote: the speaker takes "the king's picture," the face stamped on money, and makes it talk. What it says is a plea to be paid in kindness rather than cash. The idea that money has a voice, and that the voice asks for something other than money, is a quiet joke with a serious edge.
The lamb is the most tender image. It isn't "glad / to fetch money," so we can imagine something gentle being bought, sold, or sacrificed for profit and not liking it. The last two lines swerve into the everyday: "accounts / with wine and anchovies" suggests small, homely debts, the kind settled over food and drink. Judging by the title, "Fishy" plays on both the anchovies and the sense that something about money is suspicious.
The mood is wry, light, and a little uneasy. The speaker seems to prefer a world of favors and shared meals to one ruled by coins.