Educate group of fish (6)
I believe the answer is:
school
This clue is a double definition.
'educate' is the first definition.
(I know that school is a more specific form of educate)
'group of fish' is the second definition.
(I've seen this in another clue)
(Other definitions for school that I've seen before include "Teach - fishes swimming" , "streaming in here?" , "Educational facility" , "these like-minded people could follow" , "Institute of education" .)