Formed elements of blood of clupeid fish (Clupeidae) in the waters of the Central-Eastern Atlantic

A comparative study was conducted on the peripheral blood cellular composition of two mass clupeid species in the Central-Eastern Atlantic: pilchard sardine (Sardina pilchardus) and the round sardinella (Sardinella aurita). Both species are of high commercial importance but differ in their ecological preferences: S. pilchardus is a temperate-warm-water species inhabiting shelf zones and performing seasonal migrations, while S. aurita is a more thermophilic species inhabiting stable oceanic waters. The research material consisted of blood samples collected from 18 individuals during a research cruise off the coasts of Morocco and Mauritania in 2017. Hematological analysis was performed using standard protocols on stained blood smears followed by differential cell assessment. Statistically significant interspecific differences were established. A more active erythropoiesis was identified in the pilchard sardine, as evidenced by a substantially higher proportion of normoblasts (6.0±0.5% vs. 3.1±0.7% in the sardinella). This feature likely represents an adaptation to seasonal migrations on the shelf, which require efficient oxygen supply. In the leukocyte formula of the round sardinella, a significantly higher content of band neutrophils (3.9±0.3%) and segmented neutrophils (5.1±0.4%) was recorded; this may indicate enhanced innate cellular immunity, potentially associated with inhabiting warmer waters with higher microbial loads. The absence of eosinophils in both species suggests a low level of parasitic invasion in their habitats. The identified hematological differences reflect the ecological characteristics and adaptive strategies of the studied species. The obtained reference data on blood cell composition provide a basis for the bioindication of the physiological state of these key commercial fish species under changing environmental conditions.

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