Vibrating fish.. Is this normal?

[hanahandbluey]

Hello! I find my white damselfish acting weird. I don't know why she is swimming like she is vibrating or like her body's gone crazy.. Hope you could help me..

 

[Innovator]

I will assume it only displays this behavior periodically and acts quite "normal" otherwise. If you have other conspecific damselfish then it could be a breeding initiation or, if not, simply a territorial warning.