Wife’s got in mostly fish supper for working partner (11)
I believe the answer is:
Here is my best explanation:
'working partner' is the definition.
'wife's got in mostly fish supper' is the subsidiary indication.
I cannot really understand how this works, but
'in' is present in the answer.
'wife' could be 'w' and 'w' is present in the answer.
This explanation may well be incorrect...
'for' is the link.
(Other definitions for breadwinner that I've seen before include "Person whose earnings support the family", "worker", "Main earner of the family", "Sole wage earner", "Family's financial supporter", "Family's main earner", "Main wage earner", "traditional husband?", "Person bringing home the bacon" and "Rolls acquired by this".)