We made these in my after-school art class. They are a really easy ceramics project. Roll out a circle slab of clay about the size of a dinner plate. Crumple up a piece of newspaper, place it on the slab and then fold the sides up over the paper--like a taco! The paper supports the fish while you build it. Then pinch the clay together to make the fin. Next, add eyes, scales...etc.
They were kiln fired. The newspaper burns up, and then we painted them with acrylic paint.
This one is mine, and the others are from my students: