Question

fishes should not be put in water that has been boiled and cooled.why?

Answer 1

Because fishes are adapted the habit of water that are equal in temperature however, the boiled water which is very hot can roast the fish body due to extreme heat so, fishes should not be put in the water that is boiled and cooled. 

Answer 2

Fishes cant survive in de oxygenated water so but you have to re-oxygenate the water first. Either by whacking it with a good airstone for a while