Prevent artist, copper and district attorney getting fish (9)
I believe the answer is:
barracuda
'fish' is the definition.
(barracuda is a kind of fish)
'prevent artist copper and district attorney' is the wordplay.
'prevent' becomes 'bar' (bar can mean to prevent or disallow).
'artist' becomes 'RA' (Royal Academician, member of Royal Academy of Arts).
'copper' becomes 'Cu' (chemical symbol).
'and' means one lot of letters go next to another.
'district attorney' becomes 'DA' (abbreviation).
'bar'+'ra'+'cu'+'da'='BARRACUDA'
'getting' acts as a link.
(Other definitions for barracuda that I've seen before include "Voracious marine fish" , "big fish" , "Marine attacker" , "fearsome swimmer" , "Voracious tropical fish" .)