The polyp-fish is a soft-bodied sea-creature about a foot long. It has in its head an organ that forms an inflated air-space filled with gas, which makes the head appear hard and round. The rest of its body appears uninflated, and its skin is smooth. It has no fins along its body, aside from its tail, and it moves by swimming through the water. It is slow and eats shellfish
Could this fish balance horizontally in the water under realistic hydrostatics?