Any in-depth examination of these models at once reveal them to be actual aircraft models, and in most cases, possessing advanced aerodynamic designed features anyone familiar with aircraft, especially a pilot, would understand having seen test models in flight.
It is a shame the German engineers failed to recognize the leading edge curlicue features on the most prominent example for what they are in fact. A design feature found on nearly all commercial airliners as leading edge Slot/Slats. These allow extreme lift at slow speeds, and better control of an aircraft at landings and take-off. Modern airliners have them in a form as a long leading edge feature that extends out and slightly down at landings and Take-offs. These curlicues could very well be far more efficient in function than current leading edge slots.
Dave Herbert demonstrates the feature in modified form (As holes instead of curlicues here) on this rather crude 'Test' model.
Minute 6:22

Additionally it must be pointed out that none of these small models exhibit any main features of fish, for none have any feature that can link them with historical features all artists have always incorporated when attempting to display a fish.
None have a Dorsal fin, none have a Caudal fin (Tail fin extending below belly of a fish). None have scales. Lacking these the artist has nothing with which to convey the concept of a fish.
With but one exception everything seen on these models correspond with the features found on all our own fighter aircraft, not always in form (As WE may be lacking in technology), but certainly in function and in location.
These are fixed wing aircraft models.
I don't believe they are of Alien origin, nor do I believe jungle peoples had factories, materials or the foundries capable of producing the source artifacts from which these models were copied.
There is another answer, and I believe it to be most astonishing!