Question

what will happen to fish if they have lived with low oxygen and then the oxygen goes up???

Answer 1

It depends on how the species has adapted/is adapting to low oxygen. If it is a fish which typically lives with little oxygen, it will experience either an increase in quality of life or will suffer because it cant handle the buildup of oxygen. But if it was a fish that is used to a lot of oxygen, going from low oxygen to high oxygen levels will certainly better its life