“What do you get if you cross a trout with an apartment?”/“A flat fish.”

An “apartment” is called a “flat” in the United Kingdom. A riddle is:
 
Q: What do you get if you cross a trout with an apartment?
A: A flat fish.
 
The joke has been cited in print since at least 2006.
 
         
Google Books
Penguin Pocket Jokes
By David Pickering
London, UK: Penguin Books
2006
Pg. ?:
What do you get if you cross a trout with an apartment?
A flat fish.
 
Klosi Jokes
Category: Fishing jokes
Date Added: 11/10/2007
Joke: What do you get if you cross a trout with an apartment ? A flat fish !
 
Twitter
Fish Chat‏
@Fish_chat
What do you get if you cross a trout with an apartment?...A flat fish
5:35 AM - 3 May 2009
   
Google Books
Sensible Nonsense.. Frank’s Comic Pack:
Humour Pack Series
By Frank Paul
BookBaby
2014
Pg. ?:
What do you get if you cross a trout with an apartment ? A flat fish !
   
6 January 2016, Herald Express (Torquay, UK), “Jokes,” pg. 13:
What do you get if you cross a trout with an apartment? A flat fish!
   
13 November 2016, Daily Star Sunday (London, UK), “Joke Bloke,” pg. 19:
WHAT do you get if you cross a trout with a luxury apartment? A flat fish.
 
Twitter
Lucky Score‏
@LuckyScoreNet
What do you get if you cross a trout with an
apartment ?
A flat fish !
#Joke from #FishingJokes in #Jokes, #Humor and #Satire
9:51 AM - 13 Nov 2017