>>723765014
Take one out of the middle barrel. whatever you take out will mean the barrel ONLY has that in it, either carp or catfish. So you can take the "Catfish&carp" sign off the middle barrel.
Because the middle barrel only has one fish you took out, take the sign with that fishs name and put it on the middle barrel, you're still holding on to the sign that says "catfish&carp".
Now you can go to the last barrel and take off the sign that says the fish you didn't get, and put it on the previous barrel, since all signs need to be moved. Now on that empty spot put the sign that says "catfish&carp".
Since all signs had to move someplace else, placing one in the correct spot will make the other two forced to shuffle. Whichever barrel has the sign that says "catfish&carp" MUST have only one or the other based on what fish you pulled out, so that barrel can be identified correctly.
