ABSTRACT Antibiotics are frequently detected in aquatic environments, yet their effects on aquatic biota remain poorly understood. This study evaluated the toxic effects of long‐term (28 days) exposure of Rhamdia quelen to environmentally relevant concentrations of ciprofloxacin (1, 10, and 100 μg L −1 ), focusing on the gills and posterior kidney. After the exposure period, the fish were anesthetized and euthanized. Gills were collected for biochemical and histopathological biomarker analysis. The posterior kidney was sampled for biochemical, genotoxic, and histopathological biomarkers, as well as for the evaluation of apoptosis, cell necrosis, and the incidence of melanomacrophage centers (MMC). Results showed oxidative stress in the gills of both male and female fish. Exposure to 10 and 100 μg L −1 CIP induced epithelial alterations in the gills in a concentration‐dependent manner in both sexes. In the kidney, CIP exposure caused DNA damage and necrosis in females. At 10 μg L −1 , CIP disrupted the normal histoarchitecture of the renal parenchyma, and at 100 μg L −1 , necrosis was observed in both sexes. Exposure to 10 and 100 μg L −1 also led to an increase in MMC. These findings indicate that contamination of aquatic habitats with antibiotics such as CIP is an environmental concern. In addition to affecting target organisms, such contaminants may have sublethal effects on fish that could extend to higher ecological levels.
Carvalho et al. (Tue,) studied this question.