Wife’s got in mostly fish supper for working partner (11)
I believe the answer is:
breadwinner
'working partner' is the definition.
'wife's got in mostly fish supper' is the wordplay.
I cannot really understand how this works, but
'in' is present in the answer.
'wife' could be 'w' and 'w' is located in the answer.
This explanation may well be incorrect...
'for' is the link.
(Other definitions for breadwinner that I've seen before include "Family's main earner" , "worker" , "Family's financial supporter" , "Main wage earner" , "Person whose earnings support the family" .)