THESE ARE THE WAYS THE fish WILL GET STRESS.
1.some children,even some adults tap the the tank to get the fish moving.
2.in some tank the water will be violently circulated.
3.the whole water will be changed frequently.
4.thermal shock during water change.
5.fish should not be handled.
6.some agressive fish in the tank.
Make sure the fish lives without stress.this will make the fish live without sickness and live healthy.
e.rabindranath.