Math's shark is a "prop and rudder" model, with a propeller contained in the rear of the body with a duct in the bottom. The rear end of the shark is open, allowing water to go past the propeller and out the back (rather like an impeller on a jetski). The tail acts as the rudder for steering, while pitch is controlled by the two pectoral fins on the sides. The mouth even works!!
Information on this and other model radio controlled sharks can be seen at this page.