Space behind the eyes - the retraction of the head from the posterior margin of the eye to the most distant end of the gill cover.

Department of the head behind the eyes, space behind the eyes - from the back edge of the eye to the point of the gill cover furthest from the end of the snout; the gill membrane (membrana bran-chiostega), which surrounds the gill cover from behind, is not taken into account. (in pike, for example, this membrane is very wide); the spines that occur on gill covers (e.g., in ruff) are also not taken into account.