An ichthyofaunal amendment with the length-weight relations and condition factors of some endemic and invasive freshwater fishes from Western Anatolia

Küçük Menderes River drainage area is approximately 3225 km². The river is 140 km long up to where it meets the sea (Saraçoğlu 1990). The river bed has a very narrow character, and its gradient decreases as it reaches the plain downstream in the western part from the mountain area upstream in the eastern part. The river drainage shows characteristics of the Mediterranean climate, as winters are warm and rainy while summers are hot and dry (Peel et al. 2007).

In the scope of the study, to determine the fish fauna of the river drainage, the sampling was conducted seasonally at 21 stations (15 lotic and 6 lentic water resources) from the source to downstream in 2018 and 2019 (Figure 1 & Figure 2). But because of the lack of sampling of the size of the fish, just one lotic and 4 lentic water resources’ fishes were examined in the present study. The fish sampling was investigated from Akgöl, Gebekirse, and Belevi (Selçuk/İzmir), Beydağı Reservoir (Beydağ/İzmir), and Akçay Stream (Ödemiş/İzmir) (Figure 2). The map (Figure 1) was created using the Qgis v. 2.6.1-Brighton software.

Figure 1

Figure 2

A total of 379 specimens of freshwater fish species were collected from the Küçük Menderes River drainage, Western Anatolia. In the sampling carried out in seasonal periods, a Samus 725G model electro-shocker was used in lotic habitat, and standard nets were used in accordance with the criteria of “TS-EN 14757 Water Quality-Taking fish samples with dense mesh nets with changing meshes” in lentic habitats. After anaesthesia, the fish were preserved in 5% formaldehyde and stored in 70% ethanol.

The identification of the species followed Freyhof et al. (2018), Bayçelebi (2019), İlhan et al. (2021) and Yoğurtçuğlu et al. (2022)(Table 1). Due to unespied sexual dimorphism in all the fish specimens, the LWRs parameters were calculated for all specimens. In the laboratory, the total length (L) and total weight (W) of each individual were determined using a digital calliper to ± 0.1 cm, and ± 0.01 g, respectively. Regression analysis was used to determine the relationship between the total length and weight of the individuals. For the regression, the equation: W=aLb $$W = a{L^b}$$ was used (Ricker 1973). In the present formula, W Indicates the total weight (g), L shows the total length (cm), and a (intercept) and b (slope) are the regression constants (Zar 1999). The standard error of b were estimated in the analysis. Before determination of the LWRs equality, the coefficient of determination (R²) was calculated (Zar 1999), and a correlation coefficient significance control test was applied. The student t-test was applied to data to determine the growth types of the individuals (Pajuelo, Lorenzo 1998). In the study to determine the type of growth, the equation: tc=b−3SE $${t_c} = {{b - 3} \over {SE}}$$ was used (Sokal, Rohlf 1987). In the equation, the following symbols were used: t_c; t-test value, b:slope and se_(b): the standard error of the slope. In the study, Fulton’s condition factor, relative condition factor, and mean condition factor were estimated by the following equalities K_F= 100WL^-3, K_R = W(aL^b)^-1, K_M = 100aL^b-3, respectively (Froese 2006). All statistical analyses were performed in MS Excel 2016.

Recently, fish fauna of Küçük Menderes was studied in two comprehensive papers (İlhan et al. 2021; Saç et al. 2021) (Table 1). Saç et al. (2021) recognised 21 species from 50 sampling sites. Only 24 of these 50 sampling sites were located directly on the Küçük Menderes River and its tributaries, and 17 of these 21 species were determined in the river and its drainages. On the other hand, İlhan et al. (2021) recognised 13 fish species from nine sampling sites. The Petroleuciscus populations of the Küçük Menderes were identified as Petroleuciscus smyrnaeus by both studies. However, our morphologic features of our materials completely overlap with the diagnostic characters of P. ninae provided by Turan et al. (2018). Moreover, Küçük Menderes Petroleuciscus populations were recently confirmed to be P. ninae (Kaya et al. 2024). Besides, the Cobitis populations of the river were recognised as Cobitis fahireae in both studies. In addition to Cobitis fahireae, the existence of C. afifeae has also been reported in Küçük Menderes (Freyhof et al. 2018). The loach populations of the Küçük Menderes were identified as Oxynoemacheilus germencicus (Saç et al. 2021) or Oxynoemacheilus theophilii (İlhan et al. 2021); however, these populations have been recently described as a new species and named as Oxynoemacheilus eliasi (Yoğurtçuoğlu et al. 2022). Along with the above-mentioned issues, it is understood that there are 19 species still surviving in Küçük Menderes and its drainage area (Table 1).

As per Froese (2006), the regression slope (b) is typically expected to fall between 2.5 and 3.5. In the current study, the observed value of b aligns with the anticipated range. It is accepted that the proper value of b for fish is 3.0 (Hile 1936). Furthermore, the regressions were different, but lower than b < 3 in all species except both C. carpio (3.121), and C. fahireae (3.176). The highest b value was found for C. fahireae in Akgöl Lake. All the populations in the study showed isometric growth except the population of C. fahireae from Akgöl Lake, which shows positive allometric growth.

Although it is an endemic species of Western Anatolia water resources, there is still a lack of studies for local knowledge on the biological data of the S. fellowesii. In some of the limited studies, the LWRs of the species were evaluated: b = 2.760, from Işıklı Lake by Balık et al. (2002); as b = 2.802, from Ikizcetepeler Reservoir by Koç et al. (2007); in 12 different sampling station between b = 2.9 - 3.4, from Mugla Province by Top et al. (2016), b = 2.607, from Küçükler Reservoir; and b = 2.597 from Buldan Reservoir by Güçlü and Küçük (2021), which is a very recent study from the Gediz River Basin. Most of the previous studies have been discussed from the reservoirs except for Işıklı Lake (Denizli province). It was expected that the reservoirs` fish population have smaller b values than the natural ecological areas in terms of productivity differences of the reservoirs and natural water resources. In the Küçük Menderes River Basin`s water resources that have been investigated in the current study, Aktaş Stream has one of the healthy ecological habitats, and the anthropogenic pressure of on it is not big as the other resources. For these reasons (or just one of them) the b value of S. fellowesii might be greater than in the previous studies.

To date, the length and weight distribution were found to be SL_min = 4.49, SL_max = 6.08 from Akpinar Spring, and SL_max = 4.23 SL_min = 6.14 cm Gördes Creek (Gölmarmara, Manisa) for C. fahireae (Güçlü, Küçük 2015). LWRs of the C. fahireae species population from Biga Peninsula (from North-western Anatolia) was b = 3.315, for a = 0.0035 (İlhan et al. 2012). The reason for the differences of the b value of the C. fahireae might be related to the smaller sampling size of the current study (n = 5) or the anthropogenic pressure on the river drainage. The real situation of C. fahireae populations’ health in the basin needs to be investigated with further studies.

In previous studies, there has been a lack of knowledge about the invasive species of the area. The limited studies were made in one of the closest basins, the Gediz River Basin. The LWRs of the invasive species found from the Gediz River`s different water resources changed respectively between b = 3.023 from Marmara Lake and b = 4.347 from Demirköprü Reservoir for C. gibelio; and b = 3.423 from Demirköprü Reservoir and b = 3.921 from Marmara Lake for A. boyeri (Güçlü, Küçük 2021). In another study, the b value was found to be b = 2.965 (for combined sexes) for C. gibelio species from Marmara Lake (Ilhan et al. 2020). In the current study, the b value of C. gibelio was found to be b = 2.914 from Akgöl Lake. According to previous studies, the b value of the current study is smaller. It is an accepted situation that the Gediz River Basin`s ecological habitat health is better than the Küçük Menderes River Basin`s ecological habitat health, so this might be the reason for the smallest b value of the species.

The variability in the b constant value is acknowledged, attributable to diverse factors. Standardizing the sampling procedure could potentially attribute differences in length-weight ratios (LWRs) values to habitat variations (Tesch 1971). Discrepancies in b values, as observed in other studies, may be influenced by factors including water quality and nutrient availability (Sparre et al. 1989). Moreover, differences in the number of samples, sampling period, and species sampling methods may contribute to the observed variations. The characteristics of the populations might be influenced by various parameters, such as stress, environmental changes, food resources, habitat health, and disease (Pauly 1993; Petrakis, Stergiou 1995). The geographical location, environmental factors, fish health, reproduction, sex, age, and stomach ingredients are the most effective features (Wootton 1998; Bagenal, Tesch 1978). Thus, the differences in the b constant may have been related to one or more of the factors mentioned above. According to personal observations, Küçük Menderes River drainage is under anthropogenic pressure and because of this pressure it cannot save its natural habitat structure.

In terms of growth type, isometric growth was determined for all specimens at the sampled localities except C. fahireae. In the current study, S. fellowesii showed isometric growth at Akgöl Lake, which is a natural water resource (see Table 2 and Table 3; b = 2.980; t_cal = 0.653 < t_0.05, n = 187 = 1.66). In a recent detailed study, the growth type of S. fellowesii were evaluated from 12 water resources from around Muğla Province, Western Anatolia (Top et al. 2016). In the related study, 10 populations of S. fellowesii showed isometric growth, while except for both Sarıöz and Gelibolu, streams showed positive allometric growth.

In the current study, Fulton’s condition factor for all individuals ranged between 0.391 (S. fellowesii) to 3.080 (S. fellowesii); their relative condition factor ranged between 0.346 (O. eliasi) to 2.746 (S. fellowesii), respectively. Because one of the endemic species of the related study had the minimum relative condition factor values, discussing O. eliasi`s species CF might be useful. In previous studies, the condition factor of O. eliasi was studied only by Çiçek et al. (2022) as O. germencicus. As the Küçük Menderes loach populations have been described as O. eliasi (Yoğurtçuoğlu et al. 2022), we accepted and compared Çiçek et al. (2022)’s data as O. eliasi. In their study, the loaches from Kadin Stream (a drainage of Küçük Menderes River) K<sub>F</sub> varied between 0.85-1.04 (K<sub>Fmean</sub> = 0.91); their relative condition varied between 0.92-1.14 (K<sub>Fmean</sub> = 1.00) in Çiçek et al. (2022). In the current study, Fulton`s Condition Factor was found to be K_Fmin = 0.703, and K_Fmax = 1.018 (K_Fmean = 0.863); their relative condition factor varied between K_Fmin = 0.346, and K_Fmax = 1.568 (K_Fmean = 1.114). In both studies, the K_F and K_R factors seem similar. The condition factor gives important clues about both abiotic and biotic factors playing a role in the physiological condition of the fish populations. In the study, CF of fish showed that the fish species have suitable environmental parameters in their natural habitats.