Validation of growth increments in stylets, beaks and lenses as ageing tools in Octopus maya

Octopus hard structures have recently been used as ageing tools. Thirty-two Octopus maya were raised in captivity in four age groups, ranging from 124 to 233 days old. Their stylets, beaks and eye lenses were analyzed in order to validate the periodicity of growth increments during all the octopus life. Transverse sections of stylets were mounted in glycerin jelly, beaks were sagitally cut to analyze their lateral walls and eye lenses were processed by histological techniques and mounted in resin. Growth increments in each structure were observed and counted under a microscope. Stylet increments were successfully validated as their counts were closely related to age in days. Beak increments from the two younger age groups showed a close relationship with age, suggesting a daily deposition. However, persistence of lower increment counts strongly suggests that not all growth increments could be counted, probably due to erosion during feeding. Eye lens increment counts did not show a relation with age, although periodicity, if any, might be subdaily. The use of stylets is recommended for O. maya growth and ageing studies as they also showed a high precision in increment counts between readers.