A “man-eating fish” is quite different from a “man eating fish.” There’s a joke:
 
Q: Where’s the best place to see a man-eating fish?
A: A seafood restaurant.
   
“And only last week in a restaurant I found myself face to face with a man eating fish” was cited in a 1937 newspaper column. The joke began appearing in joke books since at least 1981.
 
   
Old Fulton NY Post Cards
16 August 1937, New York (NY) Post, ‘Take It From Me” by Neal O’Hara, pg. ?, col. 1:
“And only last week,” murmured the quiet little man la the corner, “in a restaurant I found myself face to face with a man eating fish.”
   
Google Books 
Smokey the Shark, and Other Fishy Tales
Compiled by Charles Keller
Illustrated by Lee Lorenz
Englewood Cliffs, NJ: Prentice-Hall
1981
Pg. 13:
Where would you see a man-eating fish?
At a seafood restaurant.
 
Google Books
The Zaniest Riddle Book in the World
By Joseph Rosenbloom
New York, NY: Sterling Publishing COmpany, Inc.
1984
Pg. 44:
Where is the best place to see a man-eating fish?
In a seafood restaurant.
 
Google Books
A Century of Psychology as Science
Edited by Sigmund Koch and David E. Leary
New York, NY: McGraw-Hill
1985
Pg. 431:
Some jokes — such as they were — turned on ambiguities of surface structure, such as
 
Where would you go to see a man eating fish?
A sea-food restaurant.
   
Old Fulton NY Post Cards
4 September 1987, The Citizen (Auburn, NY), “Mighty Funny’s Mini Jokes,” pg. 38, col. 4:
Q: Where would you find a man-eating fish?
Mighty Funny: In a seafood restaurant.
(Sent in by Eric Paolini)
 
12 December 1987, Capital Times (Madison, WI), “Send me a riddle,” Capital Times Comics pg. 1:
Q. WHERE CAN YOU SEE A MAN-EATING FISH?
A. IN A RESTAURANT.
CURT FOUST, MARK CENTER, OK.
 
Google Groups: rec.humor.jewish
Kids Puns of the Weak 09-21-04
Stan Kegel
(...)
Where is the best place to see a man-eating fish?
A seafood restaurant. (Rosie O道onnell)
 
Twitter
Ryan Charles Brown
‏@senatorbrown
Where’s the best place to see a man-eating fish?....In a restaraunt. Thank you Nesper Signs.
3:27 PM - 3 Oct 2009
 
Twitter
Gary Soup
‏@GarySoup Gary Soup Retweeted Andy Bechtel
My uncle’s restaurant joke on the kids: “Ever see a man-eating fish?” “No.” “There’s a man eating fish!” Gary Soup added,
Andy Bechtel @andybechtel
Why we need hyphens — because a lion-hunting dentist is not the same thing as a lion hunting dentist.
9:45 AM - 7 Sep 2015