Animation actions on an armature following a path problem

Hey there all,

I have a problem with a fish I’m trying to animate.

I’ve rigged it up so that a bone at the end of the tail (called tailCTRL) makes the backbones move via Action constraints on them.

But I also have the parent bone (called boneBack001) following a path, and when I start to animate the tailCTRL bone as it moves down the path then I get really jerky animation of the bones.

See my file here

Is there a reason why this is happening?

Thanks in advance.

Would it be because I’ve keyframed the backbones with Loc/Rot/Scale and you can’t have both a constraint and keyframes on bones at the same time?