Age validation in common octopus, Octopus vulgaris using stylet increment analysis

Abstract

Daily periodicity of growth increments in stylets of Octopus vulgaris Cuvier 1797 was validated from known-age laboratory-raised specimens. Daily periodicity of growth increments was corroborated by staining the stylets either with oxytetracycline or tetracycline and comparing the number of rings produced with the elapsed days. A total of 19 individuals (10 males and 9 females, 680 to 1470 g body weight) were marked with oxyetracycline injections at Vigo (mean of 124 mg oxytetracycline per Kg of octopus) and 6 individuals (1 male and 5 females, 248 to 570 g body weight) were stained with tetracycline injections at Naples (mean of 120 mg/Kg). The animals were successfully maintained in captivity until sacrificed for up to 6 (1 specimen), 9 (1 specimen), 18 (6 specimens from Naples) and 21 (17 specimens) days. Transverse stylet sections were embedded in thermo-plastic resin and polished until a thin and translucent section was achieved. Several sections of each stylet were prepared and photographed. Increments were counted 3-5 times by two different readers. Increments counts for each stylet were analysed and outliers excluded using statistical methods. The number of increments counted was 18.9 ± 1.4 and 20.5 ± 1.5 days for 18 and 21 days specimens, respectively. Mean rate of increments formation was 1.02 increments per day (1 increment = 1 day). Photograph analysis corroborated the regular deposition pattern of stylet growth increments. Consequently, this study successfully validates daily increments deposition in stylets of Octopus vulgaris to the size range analysed.