Using otolith shape for intraspecific discrimination: the case of gurnards (Scorpaeniformes, Triglidae)

• Main Authors: Stefano Montanini, Marco Stagioni
• Format: Article
• Language: English
• Published: Frontiers Media S.A. 2015-11-01
• Series: Frontiers in Marine Science
• Subjects: otolith; Shape Analysis; Morphometric analysis; Adriatic sea; Triglidae
• Online Access: http://journal.frontiersin.org/Journal/10.3389/conf.FMARS.2015.03.00143/full

The sagittal otoliths are sound transducers and play an important role in fish hearing. Triglidae (Teleostei, Scorpaeniformes) are known for sound producing ability in agonistic contexts related to territorial defence, reproduction and competitive feeding (Amorim et al., 2004). Chelidonichthys cuculus and C. lucerna show a significant body size-depth relationship and specie-specific feeding strategies with growth. Both juveniles and adults of C. cuculus prey necto-benthic invertebrates while C. lucerna specimens change diet from crustaceans to teleost during growth (Stagioni et al., 2012; Vallisneri et al., 2014; Montanini et al., 2015). The goal of this study was to analyze intraspecific shape variations in sagitta of model species of gurnards. 217 specimens were collected during bottom trawl surveys in Adriatic sea (northeastern Mediterranean). Each left sagitta was removed, cleaned in ultrasounds bath and kept dry. The otolith digital images were processed to calculate five shape indices (aspect ratio, roundness, rectangularity, ellipticity and circularity). Indices were normalised to avoid allometric effects according to Lleonart et al. (2000), than processed by linear discriminant analysis (LDA). The SHAPE program was used to extract the outline and to assess the variability of shapes (EFA method) and estimated it through the study of principal component analysis (PCA). Considering the first two discriminant functions, LDA plot showed a clearly separation between juvenile and adults for both species. About EFA, the first 4 principal component discriminated over 80% of variance and significant differences were found at critical size between juveniles and adults for all the components analysed. The allometric trends corresponded to a relative elongation of the sulcus acusticus and an increase of excisura ostii. The combined use of the two external outlines methods should be highly informative for intraspecific discrimination and might be related to endogenous (sexual maturity) and exogenous causal factors (depth, substrate, diet). In conclusion, it is important evaluate the differences in the shape of sagittal otolith during growth because these ontogenetic variations could be confused with stocks variations.