Bloater's not a bad seafood option (7)
I believe the answer is:
lobster
'seafood option' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'bloater's not a bad' is the wordplay.
'not' indicates named letters should be taken away.
'bad' indicates an anagram.
'bloaters' with 'a' removed is 'bloters'.
'bloters' is an anagram of 'LOBSTER'.
Can you help me to learn more?
(Other definitions for lobster that I've seen before include "Pincered crustacean, a delicacy" , "Crustacean caught in pot" , "one to loft a > shellfish?" , "Lets bro have the shellfish" , "Slow bowler may be" .)