Rod, pole or - fish (5)
I believe the answer is:
perch
I believe this clue is a triple definition!
'rod' is the first definition.
(I know that rod can be written as perch)
'pole' is the second definition.
(synonyms)
'or' acts as a link.
'fish' is the third definition.
(I know that perch is the parent taxon of perch.)
(Other definitions for perch that I've seen before include "Roost; old measure" , "A fish; alighting place" , "(Fishy) pole where bird sits" , "Fish and old measure" , "Roosting place" .)