It's angry about fish! (8)
I believe the answer is:
stingray
'fish' is the definition.
(type of fish)
'it's angry about' is the wordplay.
'about' indicates anagramming the letters.
'its'+'angry'='itsangry'
'itsangry' anagrammed gives 'STINGRAY'.
(Other definitions for stingray that I've seen before include "Fish with venomous tail" , "Dangerous fish" , "Flatfish with barbed spine" , "Large venomous fish -- it's angry (anag)" , "menace in the water" .)