Otoliths are calcareous structures found in the inner ear (labyrinth) of fish, responsible for hearing and balance. The labyrinth consists of three otolithic organs called the sacculus, the utriculus and the lagena, each containing chemically and morphologically different otolith pairs (La Mesa et al. 2020). In ostariophysians, lagenar and utricular otoliths are larger than saccular otoliths (Wright et al. 2002). Otolith phenotypic variation has long been used for different types of ichthyological studies, especially taxonomy (Więcaszek et al. 2020), genetics and phylogeny (Firidin et al. 2017), predator–prey relationships (Więcaszek et al. 2020), fossil studies (Gierl & Reichenbacher 2015), mass asymmetry (Yedier et al. 2018), paleoichthyology (Gierl et al. 2018), bioarchaeology (Van Neer et al. 2004), trophic ecology (Assis et al. 2020), age determination (Sun et al. 2020) and stock identification (La Mesa et al. 2020; Ozpicak 2020).
In terms of fisheries management and fish biology, it is important to determine the phenotypic variation induced by environmental factors. Being species specific, the shape and morphometry of otoliths have been used as a natural marker and a useful tool for fish identification. However, there are some limitations in research on otoliths. Since mineralization and growth of otoliths in fish are affected by environmental factors, aberrant crystallization of otoliths and fluctuating asymmetry in otolith dimensions should be investigated (Bostanci et al. 2018; Yedier & Bostanci 2019; Mejri et al 2020; Yedier & Bostanci 2020). Fluctuating asymmetry in otoliths can indicate specific environmental effects, and otolith asymmetry in fish has been used as a bioindicator to study the status of different populations (Grønkjaer & Sand 2003).
Otolith shape can vary within and between species with sex, population, growth rates and ontogenetic stages (Więcaszek et al. 2020). Although genetics and environmental conditions can strongly affect otoliths and their morphometric features, they are considered valuable structures for stock identification (Koeberle et al. 2020). Furthermore, relationships between fish size or weigh and otolith dimensions have several advantages in estimating the size of prey (Škeljo & Ferri 2012; Yılmaz et al. 2019; Saygın et al. 2020). Otoliths are often found in the stomach contents of different organisms (fish, mammals and birds) or as fossils in sediments. Therefore, species identification using otoliths is a very useful tool in food chain, ecological and paleontological studies (Buckland et al. 2017).
The genus
Research on i.a. otolith biometrics or biological properties of
Utricular (lapillus) and lagenar (asteriscus) otoliths were removed, distinguishing between left and right ones. Otoliths were removed through an incision in the cranium, then cleaned with ethanol and stored in a dry place. All otoliths were photographed on the distal (asterisci) and dorsal (lapilli) surface using a Leica DF295 digital camera. The asteriscus length (AL), asteriscus height (AH), asteriscus perimeter (AP), asteriscus area (AA), lapillus length (LL) and lapillus width (LW), lapillus perimeter (LP) and lapillus area (LA) were measured to the nearest 0.001 mm using Leica Application Suit ver. 3.8 Imaging Software (Fig. 2) and weighted (AOW for asterisci and LOW for lapilli; 0.00001 g). The length of asteriscus and lapillus otoliths was defined as the greatest distance between their anterior and posterior margins. The height of asteriscus otoliths was defined as the greatest distance between their dorsal and ventral edges. The width of lapillus otoliths was determined as the greatest distance from their lateral to medial margins (Yilmaz et al. 2015). Lapilli and asterisci pairs were also photographed on their distal and proximal sides using a Hitachi SU 1510 Scanning Electron Microscope (SEM) for their phenotypic description (Fig. 3).
All variables were tested for normality and homogeneity of variance using Kolmogorov–Smirnov, Shapiro and Levene's tests, respectively. Different tests (paired t-test, Wilcoxon test, Independent Two Sample t test, Mann–Whitney U test) were used depending on whether the data were normally distributed or not. Differences between sexes were also examined by the independent t-test. A standardized model was used to remove the size effect on otolith measurements according to the following equation (Elliot et al. 1995; Lleonart et al. 2000):
Linear and nonlinear (power) models (y = a + bx, y = axb, where y is the otolith measurement and x is the fish length) were applied to determine the relationships between the otolith morphometrics and
The asteriscus and lapillus of
Two length classes (Class I: 6.7–10.9 cm
In addition, multivariate analyses (PCA and DFA) were performed to detect morphometric differences in the shape of otoliths between mature and immature samples. Discriminant function analysis (DFA) was performed to detect differences in otolith shape variation between the sampling sites. Wilks’ lambda (λ) was employed to assess the performance of DFA.
SPSS 20, Past 3.0, Minitab 15.0 and Excel were used for statistical analysis.
The sex ratio was 1:2.02 based on the total sample size of females (n = 51; 33.12%) and males (n = 103; 66.88%). The maximum and minimum total length and weight of individuals ranged from 6.70 to 15.00 cm and from 2.58 to 33.48 g, respectively.
There are differences between females and males in terms of the total length and weight (Mann–Whitney U Test,
Descriptive statistics of otolith characteristics for Caucasian bleak by length classes
Character | Otolith length | Otolith height/width | Otolith weight | Otolith perimeter | Otolith area | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Min. | Max | Mean ± SD | Min. | Max | Mean ± SD | Min. | Max | Mean ± SD | Min. | Max | Mean ± SD | Min. | Max | Mean ± DS | ||
Class I (6.7–10.9 cm |
RA | 0.985 | 1.907 | 1.596 ± 0.15 | 1.082 | 1.991 | 1.596 ± 0.15 | 0.00036 | 0.00140 | 0.00095 ± 0.0002 | 3.500 | 6.507 | 5.591 ± 0.51 | 0.772 | 2.397 | 1.742 ± 0.22 |
LA | 0.998 | 1.915 | 1.591 ± 0.15 | 1.053 | 1.863 | 1.582 ± 0.12 | 0.00037 | 0.00143 | 0.00095 ± 0.0002 | 3.442 | 6.764 | 5.633 ± 0.52 | 0.767 | 2.362 | 1.756 ± 0.23 | |
RL | 0.919 | 1.616 | 1.420 ± 0.11 | 0.733 | 1.460 | 1.058 ± 0.10 | 0.00024 | 0.00174 | 0.00115 ± 0.0002 | 2.644 | 4.610 | 3.965 ± 0.30 | 0.506 | 1.502 | 1.128 ± 0.16 | |
LL | 0.919 | 1.678 | 1.452 ± 0.11 | 0.733 | 1.770 | 1.063 ± 0.12 | 0.00024 | 0.00183 | 0.00115 ± 0.0002 | 2.644 | 4.678 | 4.028 ± 0.30 | 0.506 | 1.553 | 1.160 ± 0.16 | |
Class II (11.0–15.0 cm |
RA | 1.356 | 2.681 | 1.782 ± 0.20 | 1.304 | 2.197 | 1.720 ± 0.13 | 0.00031 | 0.00301 | 0.00122 ± 0.0003 | 4.707 | 8.865 | 6.347 ± 0.70 | 1.224 | 3.471 | 2.094 ± 0.34 |
LA | 1.257 | 2.542 | 1.776 ± 0.19 | 1.330 | 2.290 | 1.730 ± 0.19 | 0.00032 | 0.00307 | 0.00122 ± 0.0004 | 4.117 | 9.444 | 6.267 ± 0.92 | 1.254 | 3.519 | 2.108 ± 0.34 | |
RL | 1.176 | 2.074 | 1.555 ± 0.15 | 0.807 | 1.693 | 1.154 ± 0.13 | 0.00050 | 0.00468 | 0.00155 ± 0.0006 | 3.205 | 5.959 | 4.344 ± 0.42 | 0.724 | 2.489 | 1.350 ± 0.27 | |
LL | 1.151 | 2.170 | 1.591 ± 0.15 | 0.815 | 1.770 | 1.161 ± 0.141 | 0.00050 | 0.00482 | 0.00155 ± 0.0006 | 3.206 | 6.099 | 4.409 ± 0.43 | 0.709 | 2.615 | 1.187 ± 0.28 | |
Total (N = 154) | RA | 0.985 | 2.681 | 1.67 ± 0.19 | 1.082 | 2.197 | 1.630 ± 0.14 | 0.00031 | 0.00301 | 0.00105 ± 0.0003 | 3.500 | 8.865 | 5.886 ± 0.70 | 0.772 | 3.471 | 1.879 ± 0.32 |
LA | 0.998 | 2.542 | 1.66 ± 0.19 | 1.053 | 2.290 | 1.639 ± 0.15 | 0.00032 | 0.00307 | 0.00106 ± 0.0003 | 2.117 | 9.444 | 5.880 ± 0.77 | 0.767 | 3.519 | 1.893 ± 0.33 | |
RL | 0.919 | 2.074 | 1.47 ± 0.14 | 0.733 | 1.693 | 1.096 ± 0.12 | 0.00024 | 0.00482 | 0.00131 ± 0.0005 | 2.644 | 5.959 | 4.113 ± 0.40 | 0.506 | 2.489 | 1.214 ± 0.24 | |
LL | 0.919 | 2.170 | 1.51 ± 0.15 | 0.733 | 1.770 | 1.101 ± 0.14 | 0.00024 | 0.00468 | 0.00131 ± 0.0005 | 2.644 | 6.099 | 4.177 ± 0.41 | 0.506 | 2.615 | 1.248 ± 0.24 |
(RA - right asteriscus, LA - left asteriscus, RL - right lapillus, LL - left lapillus)
The relationships between
Relationships between Lt and otolith dimensions
Variable | Linear | r2 | Power | r2 | |||
---|---|---|---|---|---|---|---|
a | b | a | b | ||||
Length | Asteriscus | 0.365 | 0.120 | 0.533 | 0.264 | 0.773 | 0.539 |
Right lapillus | 0.475 | 0.093 | 0.556 | 0.290 | 0.683 | 0.563 | |
Left lapillus | 0.469 | 0.096 | 0.565 | 0.288 | 0.696 | 0.569 | |
Height | Right asteriscus | 0.628 | 0.093 | 0557 | 0.373 | 0.620 | 0.563 |
Left asteriscus | 0.623 | 0.094 | 0.546 | 0.369 | 0.627 | 0.551 | |
Width | Lapillus | 0.369 | 0.067 | 0.392 | 0.246 | 0.627 | 0.389 |
Weight | Asteriscus | −0.0009 | 0.0002 | 0.500 | 2E−05 | 1.713 | 0.474 |
Lapillus | −0.0016 | 0.0003 | 0.488 | 8E−06 | 2.111 | 0.546 | |
Perimeter | Asteriscus | 0.886 | 0.463 | 0.581 | 0.806 | 0.835 | 0.585 |
Right lapillus | 1.346 | 0.256 | 0.550 | 0.856 | 0.659 | 0.548 | |
Left lapillus | 1.338 | 0.263 | 0.554 | 0.850 | 0.669 | 0.550 | |
Area | Right asteriscus | −0.466 | 0.217 | 0.594 | 0.093 | 1.255 | 0.610 |
Left asteriscus | −0.482 | 0.220 | 0.594 | 0.092 | 1.266 | 0.606 | |
Right lapillus | −0.407 | 0.150 | 0.524 | 0.058 | 1.275 | 0.533 | |
Left lapillus | −0.422 | 0.155 | 0.527 | 0.058 | 1.289 | 0.539 |
The medial face of asteriscus otoliths features a furrow. Although other authors used the term ‘sulcus’ to describe this furrow, the asteriscus does not look like a groove. For this reason, it is proposed that the name ‘fossa acustica’, used by Berinkey (1956) to name any furrow-like depression that exteriorly surrounds the fossa in cyprinids, is reintroduced. Asteriscus otoliths in the Caucasian bleak have serrated edges all around their periphery in both length classes. According to Assis (2003), the proximal surface has an acoustic pit (fossa acustica). The fossa acustica surrounded by a lobe (lobus major) can be easily detected in the asteriscus. However, the general shape of the lapillus is elongate. The antero- and posteromedial edges are small and rounded. In most lapilli, the antero- and posterolateral edges are well defined. In general, the posterolateral edge forms the pointed posterior end of the lapillus. The medial and posterior margins are slightly concave or rounded (Fig. 2). A bump (cranial umbo) is observed at its anterior end. The ventral region of the lapillus is convex and bumpy.
FF, C, RO, RE, AR and E were calculated for left and right asteriscus and lapillus otolith pairs separately. There were no differences in values of the shape indices for the left and right asteriscus and lapillus otolith pairs (
Descriptive statistics of shape indices for Caucasian bleak (right otolith) except Ellipticity; both right (R) and left (L) otolith pairs
Class I | Class II | Total | ||||
---|---|---|---|---|---|---|
Shape Indices/Otoliths (Mean ± SD) | Asteriscus | Lapillus | Asteriscus | Lapillus | Asteriscus | Lapillus |
Aspect Ratio | 1.015 ± 0.06 | 1.347 ± 0.09 | 1.036 ± 0.07 | 1.352 ± 0.07 | 1.023 ± 0.06 | 1.349 ± 0.08 |
Form Factor | 0.702 ± 0.06 | 0.897 ± 0.02 | 0.656 ± 0.06 | 0.891 ± 0.02 | 0.684 ± 0.07 | 0.894 ± 0.02 |
Roundness | 0.873 ± 0.07 | 0.710 ± 0.04 | 0.844 ± 0.09 | 0.705 ± 0.04 | 0.862 ± 0.08 | 0.708 ± 0.04 |
Circularity | 18.036 ± 1.69 | 14.011 ± 0.25 | 19.340 ± 1.96 | 14.105 ± 0.29 | 18.544 ± 1.90 | 14.048 ± 0.27 |
Rectangularity | 1.717 ± 0.22 | 0.841 ± 0.14 | 2.022 ± 0.29 | 1.004 ± 0.24 | 1.837 ± 0.20 | 0.905 ± 0.20 |
Ellipticity | 0.007 ± 0.03 | 0.147 ± 0.03 (R) | 0.016 ± 0.03 | 0.149 ± 0.03 (R) | 0.011 ± 0.03 | 1.147 ± 0.03 (R) |
1.826 ± 0.16 (L) | 1.967 ± 0.17 (L) | 1.880 ± 1.17 (L) |
Classification matrices for predicted group membership of
Length Classes | Predicted Group Membership* | ||
---|---|---|---|
Class I | Class II | ||
% | Class I | 81.9 | 18.1 |
Class II | 23.3 | 76.7 |
79.9% of the original grouped cases were correctly classified
There are many studies describing
Morphological characteristics of fish otoliths vary with species and fish size (Popper et al. 2005; Romero et al. 2020). The relationships between fish length and otolith dimensions are used as a basis for research in fish biology and fisheries. Linear and nonlinear functions are preferred to describe the relationships between otolith dimensions and fish size. In general, the nonlinear function is used to study the relationships between otolith morphometrics and total length of fish (Jawad et al. 2017; Yılmaz et al. 2019; Saygın et al. 2020). According to Lleonart et al. (2000), using a linear model to explain the relationship between otolith morphometrics and fish length is not useful because the independent coefficient “a” is not relevant in morphometry. There are no studies for
Relationships between fish size and otolith morphometrics are a baseline for studies of prey–predator interactions. Analysis of otoliths retrieved from the stomachs or feces of piscivorous predators can provide information on the type, size, mass and energy content of their fish prey (Więcaszek et al. 2020). Results of research on the relationships between fish length and otolith biometrics can be used to determine the size distribution of fish consumed by predators and stock discrimination (Jawad et al. 2017; Park et al. 2018). In the Selevir Reservoir,
This study provides data on biometric relationships between total fish length and otolith measurements for
Asteriscus otoliths in the Caucasian bleak have serrated edges around their periphery. The proximal surface features an acoustic pit. Mesial and lateral surfaces are convex. Otherwise, the general shape of the lapillus (Fig. 3) is consistent with the description provided by Schulz-Mirbach & Reichenbacher (2006). Bostanci et al. (2015) described the shape of asteriscus otoliths in four
The otolith shape varies from round in fish larvae to a specific shape in adults (Lagardère et al. 1995). Therefore, in many studies, including this one, data are standardized to eliminate the length and size factor (Zhao et al. 2017; Tuset et al. 2018; Saygın et al. 2020). In the present study, two length classes were established according to the stages of gonadal development and the classification score was calculated as 79.9%. In recent years, many studies have been conducted using different length classes according to morphology, ontogenetic effects and sexual variation (Capoccioni et al. 2011; Cerna et al. 2019; Carvalho et al. 2020; Teimori et al. 2020; Więcaszek et al. 2020). Waessle et al. (2003) identified a strong modification in the morphology of
Unfortunately, changes in climatic conditions, which affect the water regime, and human activities are the main threats to the basin and lakes. There are no doubts that all these negative phenomena will have a negative impact on the distribution of the species and the current status of its population. For all these reasons, it is necessary to develop a conservation strategy for
The data presented here indicate that the stages of gonadal development affect the shape of otoliths. To this end, further research will be needed on environmental factors, genetic patterns, and the relationship at the individual level between microchemical composition, which carriers information on fish life history, and shapes of otoliths.