Vésiga

One of the classic—but optional—ingredients for a coulibiac of salmon is called vésiga. It is a ropelike, gelatinous substance, actually the spinal marrow of sturgeon. The vésiga, after cleaning, must be simmered for several hours until tender. It is then chopped and looks like chopped aspic. It has a very mild, bland flavor and its principal contribution to the dish is its slightly tender but chewy texture.