[1] Due to spells of severe tympanitis in his youth, Wettstein's hearing was greatly impaired as an adult.
Here, his instructors included zoologists Karl Grobben and Franz Werner as well as paleontologist Othenio Abel.
Under Wettstein's helm, within five years, the museum's reptile and amphibian collection became one of the largest in Europe.
With Franz Werner and botanist Karl Heinz Rechinger, he accumulated a collection of vertebrates from southeastern Europe, publishing "Die Vogelwelt der Ägäis " (The Birds of the Aegean, 1938) and "Die Säugetierwelt der Ägäis " (The Mammals of the Aegean, 1941) as a result.
[1] In collaboration with others, he made important contributions to the multi-volume series "Catalogus faunae Austriae ".