Strange Behavior Of Danio

[ColR1948]

I noticed one of my Danios is acting strange, it is swimming up and down along the same spot all the time, it hardly ever leaves that area, there are other Danios in the tank as well and they are all over the place except this one.

It looks like it's on guard duty if that is a better description of the behavior.

 

[WILDER]

It can be a sign of stress so need to ask you some questions.

How many gallons is the tank please?
How many fish and which type?
Water stats in ammonia, nitrite, nitrate, and ph?
How long has the tank been set up?
How long have you had the danios?
Does the fish look pale?
Is he darting around the tank?

 

[Bugdozer]

Try bunging a fake plant in the area it patrols so it is forced to change its behaviour. It might return to normal.

 

[ColR1948]

Don't know what has happened but it has stopped patrolling now and swims about with the rest of the others.