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Age validation in common octopus, Octopus vulgaris Cuvier 1797 using stylet increment analysis

Hermosilla C1, Rocha F1 Gonzalez AF2, Guerra A2 & Fiorito G3

1Dpto. Ecología y Biología Animal. Universidad de Vigo. Spain. 2Instituto de Investigaciones Marinas (CSIC). Eduardo Cabello 6, 36208 Vigo, Spain. 3Laboratorio di Neurobiologia, Stazione Zoologica A. Dohrn, Villa Comunale, 80121 Napoli, Italy.

The new ageing methodology developed by Doubleday et al (2006) was tested in common octopus, Octopus vulgaris.  The method is based on growth increments quantification within the stylet structure. Daily periodicity of growth increments was validated by staining the stylets with Oxytetracycline and comparing the number of rings produced with the elapsed days. A total of 25 individuals (11 males and 14 females) were marked by Oxytetracycline injections (mean of 124 mg Oxytetracycline per Kg of Octopus) and maintained alive until sacrificed after 18 (6 specimens) and 21 (17 specimens) days. One specimen died on the ninth day of the experiment. 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. Age estimations were 18.9±1.4 and 20.5±1.5 days for 18 and 20 days specimens, respectively. Mean rate of increments formation were 1.02 increments by day (1 increment = 1 day) and photograph analysis corroborated daily deposition of stylet growth increments. Results showed a strong relation between the number of increments and the age of the specimens. Consequently, this study validates the use of stylets increments as a method to age Octopus vulgaris.

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