Where fish may be kept, as in part of opera (7)
I believe the answer is:
aquaria
'where fish may be' is the definition.
The definition suggests a singular noun but the answer is a plural noun.
'as in part of opera' is the wordplay.
'as' becomes 'qua' ('qua' is a Latin term meaning 'in the capacity of').
'in' indicates putting letters inside.
'part of opera' becomes 'aria' ('aria' is part of 'opera').
'qua' put inside 'aria' is 'AQUARIA'.
'kept' acts as a link.
Can you help me to learn more?
(Other definitions for aquaria that I've seen before include "Transparent fish tanks" , "display tanks" , "Tanks or buildings for fish" .)