Who Am I ?

I am a sea creature that lives underwater. My medium sized body in full of beautiful ombre colours that go from black to blue to yellow all over, but in this case my body has yellow stripes, black and white scales, blue short tail. I am found in streams, rivers, lakes, and ponds, I hide around and inside old tree stumps  and other places underwater. I can grown up to 12 inches long and about

4 1/2 pounds. Have you figured out who I am?