üzere üç mevsimde toplam 14 istasyonda yapılan örneklemelerde, serpme, elektroşoker, çeşitli göz açıklığındaki solungaç ağları kullanılarak 251 adet birey yakalanmıştır. Her bireyin çatal boy, ağırlık ve sindirim kanalı uzunluğu ölçülmüş, pullarından yararlanılarak yaş tayinleri yapılmış, sindirim kanalı içerikleri incelenmiştir. Sindirim kanalından çıkan besin organizmaları muhtemel en düşük taksona kadar tanımlanmıştır. Bireylerin beslenme şiddeti, sindirim kanalı içerikleri iki farklı yöntemle değerlendirilmiştir. C. gibelio bireylerinin omnivor olduğu ve çoğunlukla alglerle beslendiği belirlenmiştir. Sindirim kanalı içeriğinde besin çeşitliliği en yüksek yaz mevsiminde Sarımsaklı istasyonunda (2,55) en düşük çeşitlilik de yaz mevsiminde, Kumkale istasyonunda (0,70) görülmüştür. Sindirim kanalından çıkan besin organizmaları arasında Heterokontophyta ve Amphipoda üyelerinin önem indeksleri yüksektir.

This study reports the first recorded instance of Atherina boyeri (Risso, 1810) in the Bayramiç Reservoir, located on the Karamenderes Stream. Since 2005, ichthyological researches have been carried out in the Bayramiç Reservoir by various researchers, but none of them have noted the existence of A. boyeri in this reservoir. In the field studies conducted between May 2016 and July 2017, a total of 98 A. boyeri specimens was caught. In these samplings, a 70 m long and 2 m wide beach seine net with 10 mm a mesh size was used. Although a small number of A. boyeri was caught during the first observation in October 2016, more individuals were observed in July 2017. The fork length of the A. boyeri observed was between 2.7-8.8 cm and the weight ranged between 0.06-4.31 g. The bimodal length distribution of the specimens indicates that there have been multiple incidents of adult specimens entering the reservoir and that these individuals have given birth to new offspring. The translocation of A. boyeri into the Bayramiç Reservoir might have been due to unauthorized introduction by fishermen or through illegal release by anglers as fish bait. However, the distribution map of A. boyeri in inland waters in Turkey shows significant overlap with the migration routes of big waterfowl. The waterfowl might partially be responsible for the spread of the adult specimens across short distances.

Several Ponto-Caspian gobiids have expanded from their native distribution ranges to Europe and North America. As knowledge on their bio-ecological features in their native range is still limited, the trophic ecology of monkey goby Neogobius fluviatilis and Western tubenose goby Proterorhinus semilunaris was studied in three natural lakes in the Marmara Region of NW Turkey using the stable isotopes of δ 13 C and δ 15 N. In two of the lakes, the trophic niches (as the isotopic niche) of the gobies were highly divergent with co-existing native fishes, with no overlap. Moreover, mixing models suggests considerable inter-specific dietary differences. In all lakes, the trophic niches of gobies were never significantly larger than those of coexisting fishes. These results suggest that when introduced outside of their natural range, the gobies might integrate into new fish communities via exploiting resources that are underexploited by native fishes or will initially share resources with these species before their niches diverge, perhaps through competitive displacement.

An invasive species, Carassius gibelio, alters the native fish community through trophic niche competition

The ontogenetic diet shift of invasive Carassius gibelio (Bloch, 1782) was investigated in Karamenderes River, Turkey. The fieldwork was performed during summer 2012, autumn 2012 and spring 2013. The fishes were caught by electrofishing and using gill nets. Nine fork length groups were used in order to assess the ontogenetic diet shift. The gut contents were assessed by the index of relative importance that was calculated from the frequency of occurrence, numerical abundance, and volumetric analyses. The most abundant length groups of C. gibelio were 18-20 cm, 6-8 cm, and 27-29 cm length groups during summer 2012, autumn 2012 and spring 2013, respectively. The feeding intensity was the lowest in the length groups of 15-17 cm during summer 2012, in 3-5 cm length group in autumn 2012 and in 24-26 cm length group in spring. Seasonal variations were observed in the ontogenetic diet shift of C. gibelio. Large specimens consumed more animal materials during summer and more algae in autumn. There was not any significant niche overlap recorded between small and large specimens except summer. Any niche overlap between small and large specimens might be advantageous for the establishment success of invasive Gibel carp in Karamenderes River.