Ray providing home for river fish (5)
I believe the answer is:
bream
'fish' is the definition.
(bream is a kind of fish)
'ray providing home for river' is the wordplay.
'ray' becomes 'beam' (synonyms).
'providing home for' means one lot of letters goes inside another.
'river' becomes 'r' (abbreviation for river).
'beam' enclosing 'r' is 'BREAM'.
(Other definitions for bream that I've seen before include "Swimmer" , "Carp relative" , "Amber kind of fish" , "Bar me from the freshwater fish" , "Broad, thin fish" .)