I have a Fantail
which I have had 4 years.
It started an odd behavior about 1 month ago.
During the day it swims normal, but when it gets dark even with the tank light on it is on a timer. The Gold Fish goes to the top and is sometimes upside down or on one side or the other.
I also have a Black More that acts normal at all times.
Any one have any clue why it behaves this way.