Integrated Assessment of the Biological Condition of Alosa immaculata in Relation to Microplastics, Organic Contaminants, and Parasites

The pontic shad (Alosa immaculata Bennett, 1835), one of the most economically and ecologically important species for the Danube–Black Sea basin, is affected by a large variety of anthropic and biological pressures. In this study, we aimed to investigate the presence of microplastics, persistent organic pollutants (POPs), polycyclic aromatic hydrocarbons (PAHs), and endoparasites alongside biological condition indices on individuals collected from Chișcani locality from the lower Danube Romanian sector. The overall abundance of microplastics was 1.36 ± 1.8 SD particles per individual, with significant differences between the gastrointestinal tract (1.33 ± 1.32 SD microplastics/ individual) and muscular tissue (0.23 ± 0.62 SD microplastics/ individual). The median concentrations of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) were 0.560 μg/g and 0.576 μg/g, respectively, with hexachlorobenzene, heptachlor, and lindane predominating among the OCPs, while phenanthrene and naphthalene were predominant for the PAHs. The parasitological analysis identified four species of endoparasites, with Hysterothylacium sp. being the predominant genus, showing the highest prevalence, mean intensity of infestation, and abundance. No significant associations with morphometric traits or condition indices were found. Our findings document the co-occurrence of microplastics, organic contaminants, and parasites in the examined A. immaculata specimens, highlighting the need for long-term, integrated monitoring of this ecologically and economically significant species.