Dad gets right by river for fish (4)
I believe the answer is:
parr
'fish' is the definition.
(I've seen this before)
'dad gets right by river' is the wordplay.
'dad' becomes 'pa' ('pa' can be a synonym of 'dad').
'gets' means one lot of letters go next to another.
'right' becomes 'r' (common abbreviation).
'by' is a charade indicator (letters next to each other).
'river' becomes 'r'.
'pa'+'r'+'r'='PARR'
'for' is the link.
(Other definitions for parr that I've seen before include "Young salmon; Queen Catherine ---" , "Catherine --, last wife of Henry VIII" , "Wife who survived" , "Catherine ---, Henry VIII's widow" , "Young salmon - wife of Henry VIII" .)