Amber thrashed swimmer (5)
I believe the answer is:
bream
'swimmer' is the definition.
(bream is a kind of fish)
'amber thrashed' is the wordplay.
'amber' can be anagrammed to 'BREAM'.
But, I'm not sure how the anagram is indicated.
Can you help me to learn more?
(Other definitions for bream that I've seen before include "Carp relative" , "Food fish" , "Amber (anag) - fish" , "Broad, thin fish" , "Fish of the carp family" .)