Age determination in a basking shark Cetorhinus maximus (Gunnerus, 1765) by radiographic and histological approach

Age determination based on the examination of hard anatomical parts is of fundamental importance in fisheries research. The most common method used for shark age assessment is the investigation of growth rings in vertebrae. As considerable variability exists in the amount and pattern of calcification within and among taxonomic groups of elasmobranch fishes, it is necessary to adopt a species-specific approach. The aim of the study was to employ radiographic and histological approaches to determine the age of a specimen of Cetorhinus maximus caught close to Ancona (Italy). Macroscopic evaluation of vertebral centra of three different vertebral segment chosen showed some difference among the numbers of rings. X-radiographs showed from 8 to 10 rings in the different vertebral bodies selected and histology of vertebral centra permitted to enhance the visibility of growth bands and to count up to 10 vertebral growth rings confirming data obtained by macroscopic evaluation and X-radiographs. According to the data obtained and considering a growth rings pattern of two depositions per year in this species as reported in literature, the young female here checked seem to be between the 4th and 5th year.