Why do my goldfish have clamped fins only at night?

Question

I have 6 goldfish, in day they remain active swimming around the tank without thier clamped fins. But in night of about 7:30 pm they dont swim around the tank, they do but little. And they remain still with clamped fins. When I come to watch them, they just only swim a little. So whats the reason that they have clamped fins only at night but not in day? What can i do to prevent thier clamped fins at night?

PS: My goldfish are healthy they donot have any diesease.

Answer 1

They sleep at night. Some goldfish that I have owned would actually rest on the bottom of the tank at night, and yes their fins looked "clamped" or droopy at this time. It's normal as long as they "wake up" and start swimming regularly when you turn the light back on.

Answer 2

If you haven't already, I would test your water. While they may SEEM healthy, it is better to be thorough in your care.

Ammonia levels fluctuate throughout the day (hence the fish showing signs of stress only at certain times)

If all your tests come back clean, and there are no other signs of illness, then you may take into account that they may simply be at rest.

All living things need to "sleep" and many fish simply become inactive and float in order to rest.