hi

I have guppies sailfin, black widows, sword fish , cardinals, and this 1 other fish wish is blue with a long tail, the pet shop man said it was a ninga as if u put the same kind of fish with it they will kill each other.

Well my black widows keep attacking my ninga,the ninga keeps hiding as its really scared

What do i do as i dont want it to die

I have no idea what I "ninga" is? Can you describe the fish or post a photo? Could it be a betta? Black widows can be nasty fish and pester a betta.