How many bones does this have

I have been trying to make my fish model’s tail move like the image but can’t. The Model tail (not my model, red arrow is tail) in the picture has 6 polys but not sure how many bones. My fish tail now has 6 polys and 3 bones but can’t make it work like that. I think the problem may be the amount of bones but maybe 3 is oaky, just not sure. look at the image and maybe someone here who knows animation will know how many bones or how make that tail wiggle like that. mine looks too stiff. I think my weight painting is okay.