I do not know whether 20th century items from Murano sometimes had a ground base, but many 19th century weights did! But the grinding was more transluscent.
... as stated on this board...the unpolished usually mean Chinese ...
is a not a strictly accurate interpretation of things. Lots of Chinese weights have had a rough ground base and often with an indent or two in the "circlular" formation of the base. But in more recent years lots of items from China & Taiwan have a polished base! Also, there have been many makers around the world who have applied a light grinding to the base of weights - particularly studio artists where the full cost of polishing was seen as unnecessary. So, to say "unpolished usually means Chinese" is not really accurate.
As for the fish weight, I agree that it is most likely a Chinese item to which somebody (perhaps an importer or a dealer) has added a generic Murano label. These fish look rather like dolphins and the ones I have seen have been a dark colour (like a dolphin) rather than yellow, but perhaps they were made in many colours.