Parasites and Microplastics in the Gastrointestinal Tract of Alosa immaculata from the Black Sea—Implications for Health and Condition

Alosa immaculata Bennett, 1835, commonly referred to as the Danube shad, is an anadromous pelagic species of the Clupeidae family, and plays a significant economic role for countries bordering the Black Sea. This study investigates the occurrence of both parasites and microplastics in A. immaculata specimens collected from Sfântu Georghe, with the aim of assessing their potential impact on fish health. The overall physiological condition of the fish was evaluated using Fulton’s condition factor (K) to determine whether the presence of parasites or microplastics had any measurable effect. Five parasitic genera were identified, including one ectoparasitic species from the genus Mazocraes, and four endoparasitic species from the genera Pronoprymna, Lecithaster, Hysterotylacium, and Contracaecum. Microplastic analysis showed a dominance of particles measuring 1–5 mm (62.5%), with fibers and foils being the only morphological forms detected. The most common colors were black (45%), transparent (35%), blue (12.5%), and brown (7.5%). The distribution of microplastics was higher in the stomach than intestines. Our findings offer critical insights into the combined effects of parasitic infection and microplastic pollution on this key Black Sea species. The integrated methodology, combining parasite load, microplastic content, and condition factor analysis, marks a novel approach in fish health assessment.