Otolith Shape Analysis of Five Sillaginidae Species from the Persian Gulf and the Oman Sea

The discrimination power of sagittal otolith shape analysis is evaluated for five closely related sillaginid species from the Persian Gulf and the Oman Sea; (Sillago arabica, Sillago attenuata, Sillago indica, Sillago sihama and Sillaginopodys chondropus) besides the description of morphological characters using scanning electron microscopy (SEM). The identification of sillaginids is difficult due to the limited reliable diagnostic morphological characters. The otolith shape was described by six shape indices (Roundness, Rectangularity, Circularity, Ellipticity, Form factor and Aspect ratio) and Elliptic Fourier Descriptors (EFD). For all shape indices, there was at least an overlap between the two species and no one was significantly different among the five species. Based on EFD analysis all five species were discriminated (91.7%) evidencing the high taxonomic value of sagittal otolith for the studied taxa. SEM images revealed sulcus acusticus as homosulcoid with an inframedian position in all five species. S. arabica and S. sihama are characterized by having a pseudo-ostiocaudal, while S. indica, S. attenuate and Sillaginopodys chondropus have ostial mode of opening. The ostium was tubular and slightly curved in all studied species, which was more strongly curved in S. arabica. These findings suggest that the sagittal otolith shape is a reliable tool to recognize inter-specific diagnosis for sillginid species in the Persian Gulf and Oman Sea.