The most common and most likely answer to this crossword clue is the 7 letter word POMPANO
P
O
M
P
A
N
O
More clues leading to the result POMPANO
Buddy explains!

The straight part
We know that "Fish" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fish = pompano.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 POMPANO mean?
POMPANO noun- Any of various carangid fish, of the genus Trachinotus or species Alectis ciliaris, the African pompano, from coastal parts of the North Atlantic.
- An edible butterfish, Peprilus simillimus, the Pacific pompano.