FANTAIL and NORMAL GOLDFISH

Question
hi amber worman, i have two fantail goldfishes and one normal golfish in a 40 gallon tank with a filter. basically 2 -3 days ago the fishes sit at the bottom of the tank like they are hibernating all three fishes curl up together and do that. but when i enter the room or go close to the tank they swim  normally and swim at the top like they want a feed even though i fed them. they go back to thier normal behavoiur like i have seen them before. i wanted to know whether theres something wrong with them either they are sick/ill or dieing. but from their action of swiming it doesn't look like they have a problem as the look healthy. or they feel alone or cold in the tank. please can you help me! thank you for your help and guidence.  

Answer
Hello Jonny-

I'd guess that the water's pretty cold if they are curling up at the bottom. 65-70 F is best for goldfish, perhaps a light or a heater would be best if you test the temperature and find out it's low.

Also, fish DO sleep. When a fish is sleeping, it does what you have described: curl up and lay on the bottom, almost like it's dead. Once woken up, it will act normal. Maybe you are just waking your fish up during their nap time?

Hope this is helpful!
-Amber Worman