Metal pollution is one of the main environmental threats in freshwater ecosystems. Aquatic animals can accumulate these substances and transfer them across the food web, posing risks for both predators and humans. Accumulation patterns strongly vary depending on the location, species, and size (which in fish and crayfish is related to age) of individuals. Moreover, high metal concentrations can negatively affect animals’ health. To assess the intraspecific relationship between metal accumulation and size and health (proxied by the body condition) of individuals, the concentration of 14 metals (Al, As, Cd, Co, Cr, Cu, Fe, Hg, Mg, Mn, Ni, Pb, Se, Zn) was analyzed in six alien species from the highly anthropogenically altered Arno River (Central Italy): five fish (Alburnus alburnus, Pseudorasbora parva, Lepomis gibbosus, Ictalurus punctatus, and Silurus glanis) and one crayfish (Procambarus clarkii). We found that in P. clarkii, Cu was negatively related to size, as well as Al in L. gibbosus and Mg for adult I. punctatus. Positive size-dependent relationships were found for Hg in L. gibbosus, Fe in S. glanis, and Cr in juvenile I. punctatus. Only Co and Mg in S. glanis were found to negatively correlate with individual health. Since metal concentrations in animal tissue depend on trade-offs between uptake and excretion, the few significant results suggest different types of trade-offs across different species and age classes. However, only predatory fish species (L. gibbosus, I. punctatus, and S. glanis) presented significant relationships, suggesting that feeding habits are one of the primary drivers of metal accumulation.

In this study, the genotoxic and histopathological effects of olive-mill wastewater (OMW) on the tissue cells of Lepomis gibbosus were investigated. The fish were caught from Topçam dam lake (Çine/Aydın) and were exposed to the wastewater in 50-L aquariums which contained 0.5 % OMW for 3–5 and 7 days. In genotoxic investigations, a statistically significant increase was observed in the frequency of micronuclei in the L. gibbosus in experimental groups. As a result of the exposure to OMW, histopathological findings which showed a parallel increase with the amount of exposure in the gill, liver and muscle tissues were determined. In the gills, disruption of lamellae shape, shortening and breakage of primary and secondary lamellae, fusion and branching, separation in the secondary lamellae epithelium, ballooning dilation, hyperplasia in support cells and increase in mucus cells were observed. In the parenchyma of the liver, a difference in local staining, focal necrosis, haemorrhaging in necrotic areas, oedema of blood vessels, expansion in sinusoids, congestion and dilation in portal veins, deterioration of vessel walls, cytoplasmic vacuolization in hepatocytes, pyknotic nuclei, decrease in glycogen storage in hepatocytes near the central vein and aggregates of melanomacrophages were also observed. The necrosis in muscle bundles, widespread oedema between myofibrils, degeneration and separation in some muscle groups, decrease in glycogen content, intramuscular oedema and atrophy in the myofibers were determined in the experimental groups.