Quantification of the age-pigment lipofuscin in known-age octopus (Octopus pallidus): A potential tool for age determination

Stylet increment analysis (SIA) is the key method to age octopus, however, currently it is not reliable for all species. The suitability of the age-pigment lipofuscin as an alternative ageing method for octopus was examined. To determine the relationship between age and lipofuscin known-age octopus (Octopus pallidus) were reared in the laboratory from hatching to eight months old. Twenty-eight individuals at three different ages (3, 6 and 8 months old) were collected for lipofuscin analysis. The first two age groups (n = 5 each) were reared under ambient temperatures, while the oldest group (n = 18) was reared under three different controlled temperature regimes (n = 6 per treatment). For comparison, five wild O. pallidus were also collected for lipofuscin analysis and aged using SIA. Lipofuscin was analysed in the brain tissue and quantified at a commercial ageing centre using standard histological methods. Lipofuscin granules were clearly discernable in the brain tissue, and there was a strong exponential relationship between age and lipofuscin (R2 = 0.86). Lipofuscin concentration was not related to sex, temperature or body weight in same-age individuals. Except for one individual, the predicted age of the wild animals, based on the relationship between lipofuscin and age, was close to the age determined using SIA. This study is the first to report lipofuscin in an octopus species and shows that lipofuscin has excellent potential as an alternative ageing method for octopus. This research will have important applications for species which cannot be reliably aged using current ageing methods.

Research Highlights
► Lipofuscin granules were observed in the brain tissue of octopus.
► There was a strong relationship between age and lipofuscin concentration.
► Lipofuscin concentration was not related to sex, body weight, or temperature.
► Lipofuscin has the potential to be an alternative ageing method for octopus.