570 ISSN 0032-9452, Journal of Ichthyology, 2020, Vol. 60, No. 4, pp. 570–577. © Pleiades Publishing, Ltd., 2020. Otolith Shape Analysis and the Relationships between Otolith Dimensions–Total Length of European Bitterling, Rhodeus amarus (Cyprinidae) Sampled from Samsun Province, Turkey S. Saygın a, *, M. Özpiçak a , S. Yılmaz a , and N. Polat a a Ondokuz Mayis University, Atakum, Samsun, Turkey *e-mail: semra.saygin@omu.edu.tr Received November 11, 2019; revised February 15, 2020; accepted February 19, 2020 Abstract—The goal of this study is to investigate the relationships between total length and otolith dimensions and detect the otolith shape index values of Rhodeus amarus sampled from the two different localities (Terme and Terice Streams) in Turkey. A total of 116 specimens of R. amarus were collected. Power models were applied to determine the relationships between otolith dimensions and fish length. Otolith indices were calculated for asteriscus and lapillus pairs. R. amarus were studied ranged in total length from 4.5–8.9 cm for two localities. When the relationships between total length, otolith length and otolith width were examined, the best fit was obtained among total length and otolith length in two localities for both asteriscus and lapillus (r 2 > 0.705). Analysis for otolith measurements (asteriscus and lapillus) clearly demonstrated that there was a difference in terms of otolith lengths between samples of Terme and Terice Streams. However, form factor, circularity, roundness values of asteriscus and rectangularity, aspect ratio, ellipticity of lapillus are different between Terme and Terice Streams (p < 0.001). Keywords: European bitterling, Rhodeus amarus, otolith shape, lapillus, asteriscus, Samsun Province DOI: 10.1134/S0032945220040190 INTRODUCTION The European bitterling, Rhodeus amarus (Bloch, 1782), is a freshwater fish with an unusual spawning symbiosis with freshwater mussels. Bitterling are rela- tively small fish, rarely exceeding 70 mm standard length. They are relatively deep-bodied, with a body depth 29–45% of their standard length (Holčík, 1995; Reichard, 1998). European bitterling is a limnophilic species (Economidis, 1973). In addition to lakes, they are also found in vegetated rivers with low flow rates, bottom covered with fine sand and mud (Przybylski and Zieba, 2000). The systematic position and rela- tionships of the bitterling populations remain ques- tionable and controversial with poor consistency found in morphological data. In literature, there are many studies on R. amarus, but there are limited stud- ies devoted to otolith features of European bitterling. Schulz-Mirbach and Reichenbacher (2006) described the general shape of utricular otoliths. However, to the authors’ knowledge, no previous studies on otolith shape of R. amarus have been carried out. So, this study will be the first comprehensive study of the spe- cies' otolith shape analysis. Otolith morphometry may differ between populations of the same species living in different habitats (Reichenbacher et al., 2009). Therefore, the results of this study will provide data in order to compare the results of future studies on the otolith characteristics of the R. amarus inhabiting dif- ferent habitats. The sagittae are the biggest pair of otoliths and the lapilli are the smallest in most bony fishes; however, in the members of Cypriniformes and Siluriformes, the asterisci are the largest otoliths and the sagittae are the smallest (Harvey et al., 2000; Assis, 2003; Campana, 2004). Otolith analysis are used to determine fish spe- cies or stock identification, age and growth, paleonto- logical studies, life history and migration analysis of fish, estimate the original size of the ingested prey in researches on population dynamics and feeding habi- tats (Nolf, 1995; Battaglia et al., 2010; Padilla et al., 2015; Viva et al., 2015; Renán et al., 2016; Javor et al., 2017; Yedier et al., 2019). Morphometry is widely used to recognize fish stocks since it is strongly affected by the environment and the habitats that fish use (Ider et al., 2017; Mapp et al., 2017; Bostanci and Yedier, 2018). The aim of this study is to detect the relationships between the total length and otolith biometrics and determine the shape index values of Rhodeus amarus sampled from the two different localities (Terme and Terice Streams) in Samsun Province and to reveal the regional differences between the localities. The aim of the present work is to give a comprehensive descrip- tion of the otoliths of Rhodeus amarus.