i would imagine once the JD gets larger he will kill the crawfish after it sheds its shell...also heard of fish being killed by lobsters and crawfish if the fish are small enough and the lobster gets lucky.
I was always told when the crayfish molt they are very prone to being killed by the fish since their armor isnt there for that period. Also have heard stories of them nabbing the occasional fish when the opportunity presented itself. Although a 3 inch fish might be a little too big for the crayfish to handle.
Again this is just what I heard and not any personal experience so I would wait for futher opinions on this before making any decisions.
Unless the crawfish is freakishly huge, like >6-8", it wont hurt your JD, those are some tough fish. But once JD gets bigger than the crawfish I'd be concerned about it. But it was free and would make a nice meal in a few months or a year for your JD so I'd say to put him in.
Its now been a lil over a week since I put the crawfish in. The JD's only picked at him when I first put him in the tank. Now he wonders around like he owns the place, climbing over everything, and unfortunately ripping up all my live mondo grass and eating the roots. He is a very personable pet and Im glad I put him in and would recomend anybody else have one at least for a bit. hopefully I can find I nice decoration for him to hide in as he molts.
Here's some pictures of him owning the tank.
I have six dempseys at the moment 3 are 3-4inches and the others 2-3. I have pictures on the "JD Tank How Am I Doing?" Thread. The crawfish squares off with the biggest male of the tank which makes the male flAsh his dark colors. But they never actually fight. I think if they did the JD would win. It's a big crawdAd but Jack "the ripper" Daniels is a mean mug.
Well heck yea for the dempsey, but that crawfish has some serious claws going on. Id hate to lose my favorite fish at night you know?
But anyways, nice tank. And try to film it if the square off or the crawdad gets eaten.
Everytime we do a crawfish boil, we keep a couple and put them in the tank. For the most part, the fish and the crawfish ignore each other. One time I did have a problem. I had just put a large crawfish in the tank, and within 5 minutes, he had grabbed a large red hook (like a silver dollar) by the mouth and was using his other claw to jab at him, like a roman gladiator or something. I used my net to break it up and never had another problem. I currently have 6 crawfish in my 125gal.