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In hearing, why quit trials? (6)

Ross

I believe the answer is:

trouts

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'in hearing why quit trials?' is the definition.
Although both the answer and definition are plural nouns, I can't understand how they can define each other.

This is the entire clue.

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(Other definitions for trouts that I've seen before include "Plural fish, speckled, rainbow etc" , "rainbow or brown fish, optional plural" .)

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