Iran. J. Ichthyol. (2021) 8(3): 170-180 © 2021 Iranian Society of Ichthyology P-ISSN: 2383-1561; E-ISSN: 2383-0964 ORIGINAL ARTICLE Characteristics of sagitta morphology in seven goby species from the Caspian Sea (Gobiiformes: Gobiidae) Parisa DAVOODI Department of Animal Science, Abstract Faculty of Science, University of Mazandaran, Babolsar, Iran 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 Correspondence described and analysed. The goal was to investigate the usefulness and efficiency of sagitta for [email protected] 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 Article history : Received 28 August 2020 (OL/OW). The results indicated that otolith morphology and morphometry can be used as Accepted 22 July 2021 diagnostic characters distinguishing the Caspian Sea gobies. While the overall shape of otoliths Online 2sss5 September 2021 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. Keywords: Taxonomy, Otolith, Neogobius, Ponticola. INTRODUCTION food resources such as Clupeonella sp. and the Gobiidae is one of the most species-rich fish family considerable competitors for other species (Corkum et both in the Caspian Sea and among marine fishes more al. 2004). generally, with numbers of described gobies species The genus Neogobius Iljin, 1927 with three constantly increasing (Vasil'eva et al. 2016; Kovačić species, Caspian goby, N. caspius (Eichwald, 1831), et al. 2017, 2021; Esmaeili et al. 2017, 2018; Eagderi round goby, N. melanostomus affinis (Eichwald, et al. 2020; Zarei et al. 2021). Gobies play an 1831) and Caspian sand goby, N. pallasi (Berg, 1916), important ecological role in coastal ecosystems and the genus Ponticola Iljin, 1927 with seven species, because of their diversity and abundance (Zander Caspian bighead goby, P. gorlap (Iljin, 1949), syrman 2011), but their significance is often underestimated goby, P. syrman (Nordmann, 1840), ratan goby, because of their small size and low commercial P. ratan (Nordmann, 1840), Kura goby, Ponticola importance, making them easy to overlook (Patzner et cyrius (Kessler, 1874), P. bathybius (Kessler, 1877), al. 2011). The Gobies exhibit the main role in the Iranian goby, P. iranicus Vasil'eva, Mousavi-Sabet & general production of the Caspian Sea due to their Vasil'ev, 2015 and P. patimari Eagderi, Nikmehr & species diversity and unexploited stocks. In addition, Poorbagher, 2020 among other species of gobiidae, they are the main food sources for important species constitute the most percent caught of gobies in this such as sturgeon fish (Acipenseridae) and Caspian region. seal (Pusa caspica), known as the great consumers of The inner ear of bony fishes is involved in hearing, Journal homepage: ijichthyol.org DOI: https://doi.org/10.22034/iji.v8i3.538 Iran. J. Ichthyol. (2021) 8(3): 170-180 171 Table 1. Details of samples studied. N: number of examined specimens. Total lengths (TL) are given as means±standard deviation. Species N TL (mm) Ponticola patimari 20 91.40±5.60 Ponticola gorlap 30 105.41±18.98 Ponticola syrman 15 214.60±15.10 Ponticola bathybius 21 257.66±29.40 Neogobius pallasi 196 101.60±10.24 Neogobius caspius 70 98.24±9.32 Neogobius melanostomus 50 102.04±18.46 to compare the otolith morphology of more species to determine discriminating characters of otolith in each species of this family. The aims of this study were (i) to compare otolith morphology of three and four species of the genera Neogobius and Ponticola, respectively, and (ii) to analyse the ability of otolith shape to classify and distinguish the studied fish at genus and species level. MATERIALS AND METHODS Sample collection: In total 402 specimens belong to Fig.1. Light micrograph of right otolith of Ponticola patimari and its features. Scale bar = 1mm. seven species were collected and examined from the mechanoreception, and equilibrium (Popper et al. south Caspian Sea (Table 1). Fish species were 2005). The saccular otolith (sagitta), one of three measured for total and standard lengths (TL in mm) paired otoliths found within the inner ear, displays and recognized based on morphological and meristic high interspecific variation in shape and size, making characteristics following Berg (1949) and Eagderi et it useful for taxonomy and phylogeny of various al. (2020). marine teleost groups (Lombarte & Castellon 1991; Otolith preparation and imaging: The right and left Tuset et al. 2003; Campana 2004; Ghanbarifardi et al. otoliths were removed from specimens. Otoliths were 2020; Purrafee Dizaj et al. 2020; Sadeghi et al. 2020). cleaned in distilled water, remaining tissue eliminated Studies of gobiid otoliths and their use for species with 1% potassium hydroxide solution for 6h, and identification are also valuable given the significant eventually washed with distilled water. The extracted role of gobies in coastal food webs (Bell & Harmelin- otoliths were stored dry in plastic tubes. A Vivien 1983; Kovačić & La Mesa 2008). Otoliths stereomicroscope fitted with a camera was used to morphology has been used to identify various prey capture the otolith images. Each otolith was species and their size classes in the diets of predators systematically placed with the sulcus acousticus based on recovered undigested otoliths from fecal facing up and anterior margin to the left (Fig. 1). The samples (Kovačić & La Mesa 2008). Concerning magnification was adjusted depending on the size of otolith morphology, Bani et al. (2013) and Davoodi & the otoliths. Rahimian (2016) proved that differences in otolith Otolith morphology and shape indices: To describe shape among studied Caspian gobies reflect the strong the shapes of otolith outlines and other morphological taxonomic distinctiveness of otolith in these species. features, we followed the terminology introduced by However, to confidently use otolith morphology to Tuset et al. (2008) and Schwarzhans (2014). To discriminate between Caspian goby species, we need analyse shape indices using the image of each otolith, 172 Davoodi/ Characteristics of sagitta morphology in seven goby species Table 2. Shape description and shape indices of the studied fishes from the Caspian Sea, OL (otolith length), OW (otolith width), S (otolith surface). Shape description Shape index Roundness 4S/πOL2 Rectangularity S/(OL×OW) Ellipticity (OL-OW)/(OL+OW) Aspect ratio OL/OW three parameters related to the otolith dimension were statistical analyses were carried out using SPSS 21.00. measured, which consisted of otolith length (OL), otolith width (OW), and otolith surface (S) (Tuset et RESULTS al. 2003). All measurements were taken using tpsDig2 Otolith morphology: The morphological software (Rohlf 2006). Four dimensionless shape characteristics of otolith for each species were indices were calculated (Ponton 2006): Roundness, described (Figs. 2-3). Ponticola patimari: Shape: Ellipticity, Aspect ratio, and Rectangularity (Table 2). Rectangular, with one anterior ventral and one Roundness is the ratio between the actual area and the posterior dorsal projection, dorsal and ventral margin area of a circle of the same length. This factor is larger flat. Anterior region: flat, with a pointed ventral when the shape of the otolith is more circular. projection and orthogonal predorsal angle. Posterior Ellipticity indicates the proportional change of the region: flattened, with long pointed dorsal projection short and long axes from zero (a perfectly round and orthogonal postventral angle (Fig. 2A-B). shape) to close to one (a spindle shape). The aspect Ponticola syrman: Shape: Rectangular, with one ratio is the ratio between the otolith length and otolith anterior ventral and one posterior dorsal projection, width and expresses the shape tendency of the otolith; dorsal margin with broad indentation, ventral margin the more elongated the otolith of the fish, the larger flat or slightly round and dentate. Anterior region: the aspect ratio is. Rectangularity describes the oblique, with round and large projection in the ventral variations of length and width for the area with one half. Posterior region: with a median notch separating being a perfect square and smaller than