Strays discovered fish (10)

I believe the answer is:

foundlings

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'strays' is the definition.
Although both the answer and definition are plural nouns, I don't understand how they can define each other.

'discovered fish' is the wordplay.
'discovered' becomes 'found' (to discover is to find).
'fish' becomes 'lings' (ling is a type of fish).
'found'+'lings'='FOUNDLINGS'

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I've seen this clue in The Daily Express.

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