Fish, like other animals and plants, use their stored fat to rejuvenate their bodies and produce eggs.
It’s best to cool down your cool-water fish gradually as sudden changes cannot be tolerated. Placing the tank in a cool room will help complete the change in 2-4 weeks. Water temperature should be no lower than 60 degrees fahrenheit. During this period, food should be kept at a minimum and there should be shorter periods of light.
After a few weeks of winter, it’s time to start gradually increasing the water temperature and light. Maintain an increase of no more than 1-2 degrees Fahrenheit daily. Food can be increased too.
Hopefully, your fish will show their approval by laying eggs and showing their brightest colors.