Stephen,
Thank you, your images are good, very good, and so this is another mystery solved.
This fish weight is from Feigl and Morawetz (Moravka), Libochovice, pattern number 1815, and almost certainly modelled by the Czech sculptor, Karel Zentner.
This is a top quality item, and the images help to confirm the view that, between the wars, Libochovice was a producer of very fine pressed glass.
Regards,
Marcus