Mince mice with fish to create trouble (8)
I believe the answer is:
mischief
'trouble' is the definition.
(I've seen this before)
'mince mice with fish' is the wordplay.
'mince' is an anagram indicator.
'with' says to put letters next to each other.
'mice'+'fish'='micefish'
'micefish' with letters rearranged gives 'MISCHIEF'.
'to create' is the link.
(Other definitions for mischief that I've seen before include "(Playfully) destructive behaviour" , "Monkey business" , "nuisance" , "Black . . . . . . . . (Evelyn Waugh)" , "Wrongdoing, devilment" .)