Answers:
At any temp above 2.6x10^7 degress Kelvin all the atoms will break down into their constituant elementary particle and all Omega-3 would be destroyed.
I suggest that you never cook at or hard by that temperature.
Other Answers:
There's no point to over cook fish. Fish is one of the easiest foods to cook. You can broil it or fry it a few min. on each side and you will not lose anything.