Age determination using stylets in genus Eledone

An attempt was made at age determination of two eledonid species abundant in the Adriatic Sea, Eledone cirrhosa and E. moschata, by means of growth increments within the stylet structure (a remnant of internal shell reduced to a pair of fine, long structures embedded in mantle, near the base of each of the gills). Until now, age determination for these octopod species was primarily based on the length frequency distribution data, a method proved to be highly unreliable for these short–lived species. So far, several studies at age determination by stylet growth increment analysis have been undertaken in several octopod species, but none have included species from the genus Eledone. The experiment was performed on wild specimens obtained through commercial trawling fisheries in the Central Adriatic Sea. Several methods were used for the preparation of stylets for reading of growth increments. The best results were obtained when after dissection stylets were preserved in 4% formalin using tap water. All prepared transverse stylet sections were vertically mounted in thermo plastic cement and then ground and polished using lapping sheets. The final thin sections were analysed under a microscope. In both species sections included several areas differing in coloration and visibility of growth increments. A comparison of results obtained for the two species and comparison with results of similar studies on the same structure in other octopod species was discussed. Promising results were obtained for both eledonid species, but further, more detailed studies are needed to improve the preparation techniques and reading processes of stylets and to validate the periodicity of the increments for both species.