Otolith shape development in young-of-the-year chub (Cyprinidae, Squalius cephalus)

Only a very few studies have focused on the influence of age on the otolith morphometry of cyprinids. Chub Squalius cephalus (L.) is an abundant and widespread European rheophilic cyprinid. Otolith shape analysis was used in many studies to characterize diverse local populations. In the present study we have evaluated the influence of age on the shape of otoliths during the early life of Chub when reared for experiment. Features of the sagittae, asterisci, and lapilli of laboratory-hatched larvae of the chub, were investigated until day 180 after hatching. Our observations showed that the lapilli and the sagittae were both present at hatching, whereas the asterisci were formed only between 20 and 30 days post-hatching. From day 45, the shape of the lapilli and the sagittae became more complex. The lapilli took the shape of a bean whereas the sagittae became far too fragile and inappropriate for study due to its developing very thin anterior and posterior rostra. From day 45, Fourier analysis of the shape of lapilli showed significant differences dependent on age group. However, the shape of the lapilli did not differ significantly between individuals of the same age group, even if their total length was different. This result suggested that differences in individual growth rate do not greatly influence the shape of the otolith. For young-of-the-year chub, according to the link between age and otolith shape, we recommend taking this parameter into account in any study aiming to highlight a genetic or environmental regulation of the otolith form