Tackle a very soft fish (8)
I believe the answer is:
approach
'tackle' is the definition.
(thesaurus)
'a very soft fish' is the wordplay.
'very soft' becomes 'pp' (musical abbreviation for pianissimo).
'fish' becomes 'roach' (roach is a type of fish).
'a'+'pp'+'roach'='APPROACH'
(Other definitions for approach that I've seen before include "Get closer to" , "Avenue" , "Come near - means of access" , "Advance towards" , "initial proposal" .)