Modeling the age-dependent occurrence of peripheral blood erythrocyte nuclear abnormalities in freshwater fish: a case study

Erythrocyte nuclear abnormalities (ENA) serve as sensitive biomarkers of genotoxic and physiological stress in fish. However, little is known about the extent to which age influences the frequency of ENA in species with different life-history traits. In this study, we investigated age-dependent ENA frequency in the peripheral blood of six freshwater fish species (C. carassius, S. erythrophthalmus, A. alburnus, R. rutilus, A. brama, and P. fluviatilis) collected from two sites of the Styr River (Ukraine). Fish age was determined from scale annuli, while ENA were assessed using the micronucleus test. To quantify the relationship between age and ENA frequency, we applied generalized linear models (GLMs) with a Poisson error structure. Statistically significant positive effects of age were observed in S. erythrophthalmus, A. alburnus, and A. brama, indicating cumulative erythrocytic damage with advancing age. By contrast, no significant trends were detected in R. rutilus, C. carassius, and P. fluviatilis, suggesting species-specific protective mechanisms. The combined GLM further confirmed an overall increase in ENA with age. These findings highlight interspecific variability in erythrocyte nuclear integrity among freshwater fish across their lifespan and support the use of ENA data for ecological monitoring.