Yes, it might be the ominous Oodinium desease. (‘Ominous’ to me because I read a lot of this desease especially with anabantoids, but never really witnessed it with my fish. – But as I said: Wild-caughts are rather new to me.) But if it is Oodiunium, it’s a rather acute outbreak with not only some spots in he fins etc. but the whole fish covered in white ‘fur’. And all this within a few hours.
This morning, again I found at least two fish with visible infection, but these were fit enough to flee right away.
Waiting for some more advice, I will try to get me the JBL Spirohexol you mentioned. So thank you for this suggestion (would have consulted Peter’s and Martin’s book, too. But, unfortunately, I lent it to a friend some days ago.)