Morphological Differences between Invasive European Bream (Abramis brama) Populations in Reservoirs in Uzbekistan

Abstract

The European bream, Abramis brama (Linnaeus, 1758), is an invasive fish species that was introduced into the reservoirs of the Kashkadarya and Zarafshan basins in 1958 from the Syrdarya delta to increase the fish productivity of newly created reservoirs. This study compared the morphology and growth of populations inhabiting the Talimarjan and Tudakul reservoirs approximately six decades after introduction. Fifty individuals were sampled from each reservoir during 2022–2025. Meristic traits, morphometric indices based on a truss protocol, and growth reconstructed from scales were examined, followed by analysis of variance, factor analysis, and discriminant analysis. In the Talimarjan Reservoir, the length–weight relationship was W = 0.0073 × TL3.1301 (r = 0.92), with D III 9, A III 22–27, and 49–55 lateral-line scales. Reconstructed standard lengths from ages 1 to 7 were 6.8, 12.6, 16.3, 18.3, 20.2, 21.9, and 23.5 cm, respectively. In the Tudakul Reservoir, the corresponding relationship was W=0.0065×TL3.1409(r = 0.94), with D III 9, A III 22–26, and 49–55 lateral-line scales. Reconstructed lengths from ages 1 to 5 were 9.2, 15.7, 20.2, 23.3, and 25.0 cm. Five morphometric traits differed significantly between reservoirs. Factor analysis identified seven latent factors explaining 73.18% of total variance, while discriminant analysis differentiated individuals by reservoir. The populations were similar in meristic traits but differed in several morphometric characteristics and growth patterns. These results indicate clear population-level phenotypic differentiation between the reservoirs.