CIAC 10/GTP (AP) Age validation in common octopus Octopus vulgaris using stylet increment analysis

Daily periodicity of growth increments in stylets was validated in wild-caught Octopus vulgaris maintained under controlled conditions. It was corroborated by staining the stylets either with oxytetracycline or tetracycline, and comparing the number of rings produced with the number of days elapsed. In all, 19 animals (10 males and 9 females; 680–1470 g body weight) were injected with oxytetracycline in Vigo (mean 124 mg kg), and another six animals (1 male and 5 females; 248–570 g body weight) with tetracycline at Naples (mean 120 mg kg). The animals were successfully maintained in captivity until sacrificed for up to 6 (one animal), 9 (one animal), 18 (the six animals from Naples), and 21 (17 animals) days. The number of increments counted in transverse stylet sections was 18.9 ± 1.4 and 20.5 ± 1.5 for octopuses maintained for 18 and 21 d, respectively. The mean rate of increment formation was 1.02 increments per day, suggesting a periodicity of 1 increment per day in the stylet. Consequently, the results successfully validate daily increment deposition in Octopus vulgaris stylets in the size range analysed.