Fish product for a buck, perhaps (3)

I believe the answer is:

roe

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'fish' is the definition.
(thesaurus)

I cannot understand how the remainder of the clue works.

(Other definitions for roe that I've seen before include "Part of fish, sounds like go through water" , "Fish eggs; small deer" , "Swift runner" , "Caviar" , "shy animal" .)

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