Thank goodness for Stephen's reply!!
Both the photo of a Nazeing fish that I have, and the drawing in Geoff Timberlake's book, show that the lips of a Nazeing fish are pulled out from the body of the glass, whereas, most other examples, including the one that started this thread, have an extra piece/trail of glass shaped over the opening to make the lips. More often than not this is clear glass. The effect is to make it look more like a beak, although maybe a little rounded at the end.
The second major difference that I see is that there are two pairs of fins used to balance the fish on with the tail held clear above the display area - although this is difficult to visualise on the drawing, once you know, you realise that there is an angle to the one shown at the back, whilst it is not possible to show/see its pair. Even if it were one fin at the back, the tail would be held higher than the surface the fish sits upon.
Lastly, the positioning of the fin near the eye is crucial. On the example shown it is both wrong, and too small - again, see the drawing shown in Geoff's book.
Interestingly, both the fish and the horse shown in my reference are referred to as "Statuettes, or in a another language, as "Figurines" - not friggers.
The only question I have is that the reference I have spells the glass blower as Achille Ducarreaux - with an "x" at the end. Can you say which is correct Stephen, or does it depend on the language it's printed in?