How do i go about making a 3d fish for school?

My biology teacher is making us do an ecology project that involves making up an animal and creating them in 3D. I chose to make a fur-covered fish with pointy spikes all over it. But I don't exactly know how to make it 3D. I have pipe cleaners for...

spikes and felt for fur, but I want to make him wider (Not bigger, but more 3D-ish, if that makes any sense). I also have tissue paper that I was thinking of putting in the middle, but I'm not sure that would look good.

Any suggestions? =)

Try using something like styrofoam or clay. Something you can attach things to, but also sculpt. Try going to your local craft store, they often have experts in that kind of thing they can give you more ideas of materials that are good for cuting and sculpting.