Morphological surveys of the sagittal otolith of marine gobiid fish (Teleostei: Gobioidei)

The challenges fish face in intraspecific communication has resulted in adaptation in different parts of their sensory system, including the auditory system. Evidence suggests that the sensory capability is specific for each species. The otolith is a part of the auditory system of teleost fish, and plays an important role in maintaining balance and in hearing. According to previous research, the morphological variation of otoliths is a result of a synergy between genetic and environmental factors such as depth, diet, swimming, and substrates. In this research we focused to explain (1) morphological variations of the otolith of gobiid fish as an animal inhabiting both aquatic and terrestrial environments; (2) the use of this morphological variations for distinguishing gobiid fish; and (3) how communication systems adapt to the local environment. The sagittal otoliths of six species of gobiid fish were extracted and described. In the next step, we studied the sagittal otoliths using the geometric morphometrics method and shape indices. The most common characteristics of the sagitta in the studied gobies fish were the median and mesial sulcus and the absence of a clear rostrum and antirostrum. A comparison between the examined methods showed that the geometric morphometric approach was able to detect the subtle differences between gobies species. Moreover, it seems that lifestyle and vision could affect the efficiency of the auditory system, in particular the otolith shape. For example, it seems the specific otolith shape of Periophthalmus waltoni (a species that unlike other fish spends most of its time out of the water) perhaps is a result of adaptation to land and water.