Fish isn't cooked by poet (8)
I believe the answer is:
stingray
'fish' is the definition.
(type of fish)
'isn't cooked by poet' is the wordplay.
'cooked' indicates anagramming the letters (letters cooked into a new form).
'by' says to put letters next to each other.
'poet' becomes 'gray' (18th-century poet Thomas Gray).
'isnt' with letters rearranged gives 'stin'.
'stin'+'gray'='STINGRAY'
(Other definitions for stingray that I've seen before include "menace in the water" , "Large fish with tail spine" , "Poisonous spined fish" , "Fish with venomous tail" , "TV show" .)