The most common and most likely answer to this crossword clue is the 8 letter word MENHADEN
I've seen this crossword clue in The Times
M
E
N
H
A
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More clues leading to the result MENHADEN
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The straight part
We know that "fish" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fish = menhaden.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 MENHADEN mean?
MENHADEN noun- Any of several species of fish in the genera Brevoortia and Ethmidium, used for fish meal, fish oil, fertilizer, and bait.