Your fish server is made in Copenhagen, Denmark, in 1838 and assayed by Christian Olsen Møller ("M-mark" stadsguardein/ assay master 1831-1840). The zodiacal symbol of Gemini tells us that the server was assayed between the 22. May and 21. June.
The maker is probably Johan Heinrich Otto (HO), born in 1800, master in 1825 and died in 1868.