Having nothing particular to do, I'd fish (6)
I believe the answer is:
idling
'having nothing particular to do' is the definition.
I can't judge whether this defines the answer.
'i'd fish' is the wordplay.
'fish' becomes 'ling' (ling is a kind of fish).
'id'+'ling'='IDLING'
Can you help me to learn more?
(Other definitions for idling that I've seen before include "Not in gear; lazing around" , "Not at work" , "Being unoccupied" , "Doing little or nothing" , "spending lazy time?" .)