Herring or trout, say (4)
I believe the answer is:
fish
I believe this clue is a double definition.
'herring' is the first definition.
(thesaurus)
'trout say' is the second definition.
(trout is a kind of fish)
(Other definitions for fish that I've seen before include "joint strengthener" , "Eg, sturgeon" , "Aquarium" , "Cod, dab, eel and ray" , "Angle; trawl" .)