Not a goldfish, but maybe silver or bronze (5)
I believe the answer is:
bream
'bronze' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for bream that I've seen before include "Fish - English guitarist" , "River fish" , "Broad, thin fish" , "Amber (anag) - fish" , "Fish of the carp family" .)