Mean to eat mainly raw fish (8)
I believe the answer is:
stingray
'fish' is the definition.
(stingray is a kind of fish)
'mean to eat mainly raw' is the wordplay.
'mean' becomes 'stingy' ('stingy' can be similar in meaning to 'mean'**).
'to eat' means one lot of letters goes inside another.
'mainly' means to remove the last letter.
'raw' with its last letter taken off is 'ra'.
'stingy' enclosing 'ra' is 'STINGRAY'.
(Other definitions for stingray that I've seen before include "Flatfish with barbed spine" , "menace in the water" , "Marine creature with venomous tail" , "Large venomous fish -- it's angry (anag)" , "swimmer" .)