The most common and most likely answer to this crossword clue is the 5 letter word TUNAS
I've seen this crossword clue in The Guardian
T
U
N
A
S
Buddy explains!

The straight part
We know that "Various kinds of fish" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case various kinds of fish = tunas.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 TUNAS mean?
TUNAS noun- Any of several species of fish of the genus Thunnus in the family Scombridae.
- The edible flesh of the tuna.
- The prickly pear, a type of cactus native to Mexico in the genus Opuntia.
- The fruit of the cactus.