The most common and most likely answer to this crossword clue is the 6 letter word SNOOKS
S
N
O
O
K
S
Buddy explains!

The straight part
We know that "Fishes" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fishes = snooks.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 SNOOKS mean?
SNOOKS noun- A freshwater and marine fish of the family Centropomidae in the order Perciformes.
- Any of various other ray-finned fishes in several families.
- (as a gesture) A disrespectful gesture, performed by placing the tip of a thumb on one's nose with the fingers spread, and typically while wiggling the fingers back and forth.