broken back fish ?

Question
Hi there, I wonder if you can help. I have a mini-pike fish in my freshwater aquarium and I woke up the other morning to find him flapping around at almost a 90 degree angle like his back is broken ? I thought at first he was just on the way out naturally, but tioday is day 2 and he is still flapping around. I dont know whether to put him out of his misery or wait a bit longer. All my other fish seem just fine ? He is a bit of a crazy fish, he has jumped plain out of the tank a couple of times and I m wondering whether he may have just slammed to hard into the glass or something ? Hope you can help ! Thanks !!

Answer
Yea i'v had this happen with my fish before aswell, i honestly dont know the real cause to it and have never heard about it form many other fish keeps aswell. Obivously you can visually see there is somthing wrong with him and he's in pain, eventually he will die due to whatever. Usually when i euthonize my fish  (they are tropical fish) I put a bowl of water in the freezer and let it sit there until a thin sheet of ice creates overtop of the bowl then i take it out and stick the fish in there, the fish will basically shutdown due to shock, which is a fast and quick method of euthonizing which i feel is the best way to put them down in the most humaine way.