Ontogenetic changes in otolith morphology and shape analyses in Chelidonichthys cuculus (Linnaeus, 1758) and Chelidonichthys lucerna (L., 1758)

Otolith growth is a complex phenomenon integrating various factors that can be considered either as endogenous or exogenous, although they are always regulated by the physiology of the fish. The material incorporated into otoliths is not reabsorbed or subject to metabolic reworking, and growth is continuous. Thus otoliths are considered as very useful tools to study the various events that characterize fish life cycles. The otolith shape is species-specific and may vary within each species according to endogenous factors (size, sexual maturation), environmental factors (use of habitat, depth distribution) and individual factors. The ecomorphological link hypothesis of the otolith shape was carried out in relation to the life history, biological and behavioral characteristics of fish species, or the type of swimming activity (Lychakov & Rebane, 2000). Chelidonichthys cuculus (Linnaeus, 1758) and Chelidonichthys lucerna (L., 1758) are the two most-landed species of Triglidae (Teleostei, Scorpaeniformes) in Italian trawl fisheries. Triglidae are known for their sound producing ability in agonistic contexts related to territorial defense, reproduction, and competitive feeding also associated with growth. A previous study on sulcus acusticus morphometrics showed higher mean values of sulcus area/otolith area (S:O) ratio of adults than of the juveniles for C. cuculus. The crystals on sulcus acusticus were different in shape, size and arrangement between juveniles and adults. In juveniles the crystals were quite enmeshed in the otolith matrix and showed a rod/smooth-shape. The crystalline arrangement of adults became more complex and with a larger, rod/rectangular-shape and well-formed faces. These differences were associated with several changes in depth distribution, diet and physiology and a consequently different use of the auditory system with ontogeny. The aim of this study was to analyze the morphology and shape variations in otoliths (through geometrical indices and elliptic Fourier descriptors [EFDs]) of these two Mediterranean gurnards in order to use otolith as phenotypic markers for significant life stages