Goldfish sleeping habits

Question
Hi Lindsay,

I have a new 10 gallon tank with a 2 inch comet goldfish (lost the other one to new tank syndrome probably).  At night,the fish has been going into a small rock cave I have in there.  I was wondering if it is sleeping there or is it a sign of it being sick.  What do goldfish usually do when they sleep?

Thanks for your help.

Answer
Hi Bela,

I'm sorry you lost your fish!  The other one, from what you describe, seems to be acting normally, though.  Goldfish don't actually sleep in the way that you and I do; fish have something a bit different.  They are diurnal, meaning that they are active both in the day and night, and instead of sleeping go into a sort of trance-like state.  Larger fish have the ability to shut down half of their brain at a time to let that rest, and then switch to let the other side rest, so they are at least half awake at all times.  (Helps them avoid being eaten.)  I'm thinking this is probably what goldfish do, if not exactly that then probably something similar.  But I think you're right, he probably is going into the rock cave to rest.

I hope this helped, let me know if there's anything else I can do for you!

-Lindsay