Do well with fish, catching ninety (5)
I believe the answer is:
excel
'do well' is the definition.
(I've seen this before)
'fish catching ninety' is the wordplay.
'fish' becomes 'eel' (eel is a kind of fish**).
'catching' is an insertion indicator.
'ninety' becomes 'xc' (roman numeral).
'eel' placed around 'xc' is 'EXCEL'.
'with' is the link.
(Other definitions for excel that I've seen before include "Predominate in" , "Do really well, outshine others" , "Distinguish oneself - XL" , "Surpass; shine" , "Be outstandingly proficient" .)