Fascinating Captain

Background:
My Fish are currently residing in a 90gal tank in the basement because I had to tear down the 180 on the second floor so they could refinish our hardwood floors. I have the same two cannister filters in the 90 that I was running in the 180 - 1 is an Eheim Pro 4+ 600 set at about 50% output strength, the other is an Eheim Wet/Dry cannister (the larger of the two models they used to make). Both output through spraybards on the back top of the tank with the water stream pointing slightly up and to the front. So, 1 side has a constant spray, 1 side has an ebb/flo spray. Last bit, I have a Current led light that I had set for a cloudy evening.

As I started shutting down the lights I observed that some of the fish seemed to prefer the steady flow output and some seemed to prefer the ebb/flow of the wet dry as there were groups on either side of the tank. It seemed as though some fish would sit on one side for awhile then move to the other while some stayed on the one side only. So I turned off all the basement lights and observed them in the dark. What I saw I found fascinating.

The group in the steady flow output of the Pro4 all faced in one direction and assumed a schooling formation, while the fish on the wet dry output side did not fall into and apparent regimented activity - they seemed to just cruse around as they pleased. What I found next though blew my mind

It seemed like every time the LED would emulate a cloud passing overhead, 1 fish from each group (usually, sometimes from just one group) would break off and move to the center of the tank. They would remain there until the next cloud passed over and then usually move to the opposite side from which they had started from (only once did I observe fish return to the side they had started from). It was hypnotic

I watched for quite awhile and the activity remained the same the entire time, it was like a rotation from one water flow condition to another. The White Butterfly was constantly changing sides, while the male Heckel Cross preferred to stay in the steay flow during the entire operation. Others move randomly back and forth at varying frequencies.

I'm going to have to figure out how to take a low light video and post it.

Don't know if anyone else has ever noticed this activity or not. In the 180gal tank I never noticed these same fish acting this way, but in the 90 gal it was like a ballet being performed - and they looked gorgeous with the moon lighting making them somewhat irridescent.

Really cool :grin: