Characteristics of sagitta morphology in seven goby species from the Caspian Sea (Gobiiformes: Gobiidae)

In this study the sagitta morphology of seven species of Gobiidae including three species of the genera Neogobius and four Ponticola, inhabiting the southern part of the Caspian Sea was described and analysed. The goal was to investigate the usefulness and efficiency of sagitta for species identification. The morphological analysis was based on four shape indices, roundness (4S/πOL2 ), rectangularity (S/OL×OW), ellipticity (OL-OW/OL+OW), and aspect ratio (OL/OW). The results indicated that otolith morphology and morphometry can be used as diagnostic characters distinguishing the Caspian Sea gobies. While the overall shape of otoliths differentiated the genera, the differences in the shape of the dorsal rim and development of posterior dorsal and anterior ventral lobes were particularly important for inter-specific distinction. The discriminant analysis could separate the specimens of genus Ponticola and Neogobius with 61% and 82% classification successes, respectively, proves that otolith shape indices were a more efficient tool for discrimination of otoliths in Neogobius than Ponticola species. Cluster analysis based on otoliths shape indices showed two main clusters, one cluster contains Neogobius species with higher roundness values, possessed more rounded shaped otoliths and the other includes Ponticola species with spindle and elongated shaped otoliths, except P. bathybius, recognized P. bathybius and Neogobius melanostomus as more similar taxa. These results were consistent with the phylogeny of these species proposed by recent molecular studies and indicated that otolith characteristics are partly genetically encoded and therefore have phylogenetic signals. The current research revealed a high degree of morphological variability of otolith shape in different species and confirmed its usefulness in Gobiidae taxonomy and phylogeny.