Trout confused with British fish (6)
I believe the answer is:
turbot
'fish' is the definition.
(turbot is a kind of fish)
'trout confused with british' is the wordplay.
'confused with' is an anagram indicator.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'trout' with its letters mixed up with 'b' gives 'TURBOT'.
(Other definitions for turbot that I've seen before include "[SOMETHING FISHY]" , "Type of fish" , "Expensive flatfish" , "Flatfish - trout B (anag)" , "Large brownish European flatfish" .)