Dan... you are already tossing in the kind of remark I asked to be avoided,

Lamarck? No...not really. It's easy to see why some would think that way, but Lamarck never dealt well with the mechanisms of change. One doesn't inherit bigger muscles as such, but merely the capacity to develop them. Those fish seemed to actually experience small, though basic, DNA changes. An individual fish might, thru practice, increase its breathing capacity, but ability to breath better in successive generations 'without practice' requires actual evolving mechanisms. Research & DNA sequencing is required to sort out which ones.