As suggested, your fish is one of the Poisson Volant figures, originally produced by Inwald. These have a ground bung/ stopper type base to fit into a glass frog and were certainly in production in the mid to late 30s and also for many years after the war. I can't say whether or not they were ever offered as car mascots - I suspect yours may have just become separated from its bowl so the owner fashioned a stand/ holder for it. The example on the website you linked to (
http://www.mascot-mania.co.uk/orphanage.html?/zzsalmon.html&19orphan57) is described as a fake because of the spurious Warren-Kessler mark. I would also disagree with the comments made that it is 'worthless' and 'mass produced'. Flower frogs are quite collectable, and there's no significant difference in production technique between these figures and the glass mascots that fetch thousands.
Equally, it's not entirely beyond the realms of possibility that these were used by some as mascots back in the day, it's just that I've seen no evidence for it. In fact, many of the Lalique and Sabino figures that are always described as car mascots were also available as paperweights/ stand alone figures. It seem that the premium associated with vintage automobilia means that they are all now catalogued as mascots, whether or not they were ever mounted on a car...