Age determination of Loligo vulgaris and Loligo forbesii using eye lens analysis

Eye lens of 196 Loligo vulgaris and 205 Loligo forbesii collected by trawl surveys from 2013 to 2015 in Sardinian waters (Mediterranean Sea) were analysed for age determination. In an alternative to the technique previously used in Sepia officinalis and Enteroctopus megalocyatus, in this study, we proposed the elimination of decalcification and dehydration steps to reduce the time of lens processing. In addition, lenses were included in epoxy resin, which was then subject to lapping, to ensure clear reading and counting of the increments. The number of increments counted in L. vulgaris (59–520) and in L. forbesii (51–543) was strongly related to mantle length and weight of the animals, with no statistical differences between the sexes. Assuming daily growth increments, L. vulgaris was estimated to have a life span of 17 months for males and 14 months for females, while L. forbesii males had an estimated life span of 18 and 16.5 months for females. The exponential model was the best fit for growth data for both species and sexes, showing higher growth for males in comparison with females. These results preliminarily indicate that the eye lens is a valid tool for age determination of the two Loliginidae species, but it would benefit from validation by additional studies.