The most common and most likely answer to this crossword clue is the 8 letter word DRAGNETS
I've seen this crossword clue in The Daily Telegraph
D
R
A
G
N
E
T
S
Buddy explains!
The straight part
We know that "fish caught by these" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fish caught by these = dragnets.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 DRAGNETS mean?
DRAGNETS noun- A net dragged across the bottom of a body of water.
- (law enforcement) Heightened efforts by law-enforcement personnel to capture suspects.