Swimmer turned amber (5)
I believe the answer is:
bream
'swimmer' is the definition.
(type of fish)
'turned amber' is the wordplay.
'turned' indicates anagramming the letters.
'amber' anagrammed gives 'BREAM'.
(Other definitions for bream that I've seen before include "Broad, thin fish" , "River fish" , "Fish - English guitarist" , "Amber (anag) - fish" , "Fish of the carp family" .)