Due to steam bath, did perch and tuna lose bones? (5)

I believe the answer is:

sauna

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'bones?' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for sauna that I've seen before include "Steam-heated room" , "Where one is sweaty" , "A Scandinavian steam bath" , "Finnish steam bath" , "Very hot room for cleansing, of Finnish origin" .)

I've seen this clue in the Sydney Morning Herald.

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