The most common and most likely answer to this crossword clue is the 7 letter word HALIBUT
I've seen this crossword clue in Financial Times
H
A
L
I
B
U
T
More clues leading to the result HALIBUT
- Prince with one and only — a tasty swimmer!
- Article 21 in shed, an alternative to 8?
- Seafood from Bali cooked in cabin
- Fish in Bali processed in shed
- Fishtail seen on a badly built fish
- A politician opens shelter for bottom dweller
- Swimmer initially has the greatest objection
- Fish skipping bail in basic accommodation
- Some narwhal I butchered to get seafood
- Occupants of sea shanty having a little party
Buddy explains!

The straight part
We know that "Occupants of sea" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case occupants of sea = halibut.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 HALIBUT mean?
HALIBUT noun- A large flatfish of the genus Hippoglossus, which sometimes leaves the ocean floor and swims vertically.