Crossword Genius

Trains fish (7)

Ross

I believe the answer is:

schools

I'm a little stuck... Click here to teach me more about this clue!

'trains' is the definition.
(I know this)

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for schools that I've seen before include "Coaches, trains" , "dolphins in groups, for example" , "Colleges" , "Educates" , "Institutions of learning" .)

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