The most common and most likely answer to this crossword clue is the 7 letter word KIPPERS
I've seen this crossword clue in The Daily Telegraph
K
I
P
P
E
R
S
Buddy explains!

The straight part
We know that "these fish" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case these fish = kippers.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 KIPPERS mean?
KIPPERS noun- A split, salted and smoked herring or salmon.
- A male salmon after spawning.
- (RAF World War II code name) A patrol to protect fishing boats in the Irish and North Seas against attack from the air.
- (naval slang) A torpedo.
- (often with capital) A member or supporter of UKIP (UK Independence Party).