Aegean Fish Assemblage: Body Shape Analysis Reveals Lessepsian Invader Traits

The Lessepsian round herring Etrumeus golanii is increasingly recorded in the Aegean Sea, but its body shape has not been quantitatively compared with that of native small pelagic fishes occurring in the same assemblage. In this study, the body shape of E. golanii, Engraulis encrasicolus, and Sardina pilchardus was examined using 281 specimens collected from the same purse seine haul in the southeastern Aegean Sea. Twelve homologous landmarks were analysed using geometric morphometrics, and 25 truss distances were used to describe the anatomical basis of shape differences. Model-adjusted body shape differences were detected among the three species in analyses including centroid size. The largest adjusted Procrustes distance was observed between E. golanii and E. encrasicolus, whereas E. encrasicolus and S. pilchardus were more similar in shape. Shape differences were distributed across several connected anatomical regions, including the head, body depth, posterior trunk, and caudal peduncle. Centroid size overlap was very limited between E. golanii and E. encrasicolus and absent between E. golanii and S. pilchardus. Given the lack of overlap between E. golanii and S. pilchardus, the observed difference was interpreted as a model-adjusted estimate rather than a direct empirical comparison of size-matched specimens. The interaction between species and centroid size was statistically significant but accounted for only 0.27% of total shape variation. These results provide a quantitative description of the morphological position of E. golanii relative to co-occurring native small pelagic fishes within the sampled southeastern Aegean assemblage.