Fish in the Strait (4)

I believe the answer is:

bass

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'fish' is the definition.
(bass is a kind of fish)

I can't explain the rest of the clue.

(Other definitions for bass that I've seen before include "Lowest male singer" , "Scottish rock" , "Fish (which sings?)" , "Fish for the low-voiced" , "Performer" .)

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

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