how long can fish go without food?

i have a pond, its going into winter and the water is cold maybe 40 or lower, does not eating below 40 degrees only applies to koi or all fishes? cause i got other fishes too like bass, bluegills, ect. they all aren't very active and just hiding in the plant all day(they do come out once in a while), r they hibernating? except 2 bluegill they still hang out
 
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