Plant found by fish next to part of canal network (8)
I believe the answer is:
charlock
'plant' is the definition.
(charlock is a kind of plant)
'fish next to part of canal network' is the wordplay.
'fish' becomes 'char ' (char is a kind of fish).
'next to' says to put letters next to each other.
'part of canal network' becomes 'lock'.
'char'+'lock'='CHARLOCK'
'found by' is the link.
(Other definitions for charlock that I've seen before include "Plant growing wild" , "Wild Mustard" .)