Clarias gariepinus

B, Özgür Emiroğlu, B, Sercan Başkurt, B, Sadi Aksu, Giannetto, Daniela & B, Ali Serhan Tarkan, 2018, Standard weight equations of two sub- / tropic nonnative freshwater fish, Clarias gariepinus and Oreochromis niloticus, in the Sakarya River Basin (NW Turkey), Turkish Journal of Zoology 42 (6), pp. 694-699 : 697

C. gariepinus and O. niloticus across the Sakarya Basin is suggested. A further result of the study was the estimation of length-length and total length-weight equations for C. gariepinus and O. niloticus from the Sakarya River Basin.

Previous studies on length-weight for C. gariepinus from its native Turkish range are available in the literature: Yalçın et al. (2002) reported a value of b of 2.82 (length range: 12.0– 82.6 cm) from the Orontes River, whereas Özcan (2008), examining samples collected from the Hatay commercial fish market, reported a b value of 2.967 (length range: 18.2–47.0 cm). In this study, the value of b for the length-weight relationship was estimated as 2.923 (length range: 15–71.7 cm) for the sample from the Sakarya River Basin. The differences may be due to the dissimilar length ranges and sample sizes, but it cannot be ruled out that differences in b values could illustrate different growth rates between native and translocated populations. In this regard, Turan et al. (2005) reported high morphologic differentiations among six populations of C. gariepinus from Turkey with the sample from Sakarya highly diverging from the other populations and they suggested that those differentiations may be related to different environmental conditions of the Sakarya River, though the species is widely tolerant to extreme environmental conditions.

For O. niloticus the b value of the TL-W in the Sakarya River Basin was 3.16 (length range: 8.0– 28.9 cm). To the authors’ knowledge, no previous data on O. niloticus from Turkey have been available in the literature. Comparing the value of b with the data reported on FishBase (www. fishbase.org) for populations of O. niloticus from other countries, it is possible to underline that all the samples with similar b values (and similar length ranges) refer to nonnative populations.

Due to the risks of new introduction, acclimation, and competition with native/endemic species, especially under the condition of climate change predicted for Turkey ( Tarkan et al., 2017), the potential impacts of these two species are expected to be exacerbated. Therefore, it is essential to monitor and manage their spread throughout Turkey and investigate their impact on native fish communities. To this end, assessment of well-being could be a useful tool to investigate the general status of nonnative populations and the degree of adaptation to new environments. Indeed, body condition indices have already been successfully used to assess the impact of nonnative species on natural and endemic species ( Giannetto et al., 2012a; Gaygusuz et al., 2013). The current findings might also be particularly important for future eradication practices by giving priority to the populations in relatively higher conditions.

Overall, further specific studies are encouraged to better investigate the characteristics of these species in the Sakarya River Basin and to collect data on other populations of the species from Turkey. Such information can contribute to the development of specific management plans aiming to minimize the impacts of these species on native fish communities and environments.

Acknowledgment

This study was produced through the support by the Çifteler Municipality and the Research Fund of Eskişehir Osmangazi University with the project entitled “Support the native fish populations through the suppression of invasive freshwater fish species, in the Sakarbaşı in Çifteler ” and coded 2016-1099 .