What causes fish against glass?

[NotReefsafe]

It seems that in many of the big tanks I see, the fish are all grouped together on one side of the aquarium, right against the glass. What causes this? Why does it only happen in some tanks?

Just curious...thanks!

 

[Jekyl]

The fish against the glass are trying to stay away from the tank boss possibly

 

[Rick's Reviews]

It seems that in many of the big tanks I see, the fish are all grouped together on one side of the aquarium, right against the glass. What causes this? Why does it only happen in some tanks?

Just curious...thanks!

Any pictures? Maybe flow too high?

 

[ying yang]

Maybe see person enter room and think it feeding time so all huddle together under or near part off tank they usually fed from or as other fish moving to different parts of tank,they all move in unison incase think missing out ^_^
Could be lots of reasons though.
More food,safer as more rocks,flow,light to bright or to dark,big worms/predators other side off tank,etc etc