Fish in small river for religious type (6)
I believe the answer is:
shaker
'religious type' is the definition.
(I've seen this before)
'fish in small river' is the wordplay.
'fish' becomes 'hake' (hake is a kind of fish).
'in' indicates putting letters inside.
'small' becomes 's' (abbreviation - e.g. clothes size).
'river' becomes 'r' (abbreviation for river).
's'+'r'='sr'
'hake' going within 'sr' is 'SHAKER'.
'for' acts as a link.
(Other definitions for shaker that I've seen before include "One gets agitated" , "Member of a Christian group practising celibacy" , "Cocktail mixer" , "Religious type" , "who plays tambourine?" .)