Buoyancy of the Cuttlefish

Abstract

IT is generally recognized that the cuttlebone not only serves the cuttlefish, Sepia officinalis (L.), as a skeleton but also gives it buoyancy. The cuttlebone contains gas spaces which give it a density of about 0.6. It is also known that cuttlefish kept in aquaria sometimes tend to float at the surface and appear to be lighter than sea water. Our experiments show that cuttlefish do change in density, and the difference between a ‘light’ and a ‘heavy’ cuttlefish is almost entirely due to a difference between the densities of their cuttlebones, the density and volume of the rest of the animal remaining almost constant.