"Rainbow" or "speckled" fish (5)
I believe the answer is:
trout
I believe this is a double definition.
'rainbow' is the first definition.
(I've seen this before)
'speckled fish' is the second definition.
(I've seen this in another clue)
(Other definitions for trout that I've seen before include "Irritating old person" , "Unattractive old woman" , "Fish (associated with Schubert?)" , "unpleasant old woman" , "Commonly caught fish" .)