Swears about the tropical marine fish with strong teeth (6)
I believe the answer is:
wrasse
'swears about the tropical marine fish with strong teeth' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for wrasse that I've seen before include "catch in the deep" , "Swears about the tropical marine fish with strong teeth" , "Bright marine fish" , "Fish - swears (anag)" , "Swimmer" .)