Hi,
Your fish server was made by Johan Herman Krohn Rønneberg (1818-95) in Ålesund, Norway.
Johan Rønneberg became a prolific master in Ålesund in 1847, after he had been a journeyman in the Norwegian town Bergen by his relatives, the Krohns - a goldsmith family and later by Monclair's in the same town. He even was in Hamburg. He was a skilled engraver and silver chaser.
He produced a lot of good silver objects, but in 1875 he retired and then on he was titulated as gold- and silver worker". He died in 1895.
Ref: Jonson Dale, Bjørn (1992),
Gullsmeden i gamle dagar: Sunnmørsk verk og virke i laugstida. http://www.soga.no/bjodale/gullsmed.htm" onclick="window.open(this.href);return false;
The server with an example of rocker engraving or wrigglework was made between 1847 and 1892, when the 830S standard was introduced.
Best regards/JAKJO