Crossword Genius

Prime collection of fish (6)

Ross

I believe the answer is:

school

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'prime' is the definition.
(thesaurus)

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(Other definitions for school that I've seen before include "group of dolphins, for example" , "Institute of education" , "For the education of fish" , "A number of fish" , "Group of sea creatures" .)

I've seen this clue in The Globe and Mail.
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