The most common and most likely answer to this crossword clue is the 8 letter word BATTERED
I've seen this crossword clue in The Guardian
B
A
T
T
E
R
E
D
More clues leading to the result BATTERED
Buddy explains!
The straight part
We know that "Fish could be/very tired" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fish could be/very tired = battered.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 BATTERED mean?
BATTERED verb- To hit or strike violently and repeatedly.
- To coat with batter (the food ingredient).
- To defeat soundly; to thrash.
- (usually in the passive) To intoxicate.
- To flatten (metal) by hammering, so as to compress it inwardly and spread it outwardly.
- To slope (of walls, buildings etc.).
- Beaten up through a lot of use; in rough condition; weathered.
- Beaten repeatedly or consistently; beaten up.
- Coated with batter.