Human beings are hot-blooded, meaning we have to get energy in form of food in order to maintain and stabilize our temperature.
Fish are cold blooded, their temperature is controlled by the environment they re in.
The metabolism of fish is controlled by their surrounding temperature. The lower the temperature, the lower the digestive time. So do patches of fungus, mold, hairworms, and rising nitrates. Lower dissolved oxygen levels and declining pH are also common. This pollution is caused with no benefit to your fish.