The most common and most likely answer to this crossword clue is the 9 letter word SHELLFISH
I've seen this crossword clue in The Daily Telegraph
S
H
E
L
L
F
I
S
H
More clues leading to the result SHELLFISH
- Seafood from Hull is served in fine hotel
- What male angler will do on front to secure catch?
- Drunkenly outspoken, narcissistic creature in the main
- Small fellow eaten by diabolical sea creature
- Hot into retail angle with oysters, maybe
- Hermit, perhaps, not considering others, adopting hard line in separate instances
- Fell out tucking into kebab – it isn’t kosher
- She fills troubled hearts, gets some sea food
- Drunk’s hogging oysters?
- The woman will search for oysters, maybe
Buddy explains!

The straight part
We know that "oysters" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case oysters = shellfish.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SHELLFISH mean?
SHELLFISH noun- An aquatic invertebrate having a shell, such as a mollusc or crustacean, especially when edible.