The most common and most likely answer to this crossword clue is the 4 letter word CRAN
C
R
A
N
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The straight part
We know that "fresh catch" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fresh catch = cran.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 CRAN mean?
CRAN noun- A measure of herrings, either imprecise or sometimes legally specified. It has sometimes been about 37½ imperial gallons, or 750 herring on average.
- (by extension) A barrel made to hold such a measure.
- An embellishment played on the lowest note of a chanter of a bagpipe, consisting of a series of grace notes produced by rapid sequential lifting of the fingers of the lower hand.