Large Intraspecies Variation in Stable Isotope Composition of the Muscle Tissues in Fish of the Genus <i>Cyprinion</i> (cyprinidae) from Middle East

Significant individual variation of nitrogen and carbon isotope composition (δ 15 N and δ 13 C values) in white muscle tissues was found in samples of three cyprinid fish species, Cyprinion macrostomus (periphytonophage), Cyprinion kais (benthophage), and Luciobarbus schejch (omnivore), collected in a small tributary of the upper Tigris system (Turkey). In particular, exceptionally low value (1.7‰) and abnormally wide intraspecific variability (from 1.7 to 15.8‰) of δ 15 N were observed in C. macrostomus . Despite samples were collected synchronously and syntopically, very broad range of δ 15 N values points out possible heterogeneity of the samples. The studied watercourse is located in the zone of agriculture with intensive chemicalization and pollution of the river by mobile forms of nitrogen (mostly ammonium) could play a significant role in lowering δ 15 N values, especially in the periphytonophage. Along with that, fish with high (normal) δ 15 N values are supposedly recent migrants that came from a large river for joint spawning with resident fish. The pollution of water bodies as well as the presence of migrations should be taking into account in stable isotope analyses-based studies on trophic ecology of fishes.