Voracious marine fish (9)
I believe the answer is:
barracuda
'voracious marine fish' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for barracuda that I've seen before include "fearsome swimmer" , "big fish" , "Voracious marine fish" , "Large predatory sea fish" , "Voracious tropical fish" .)