Effects of Fe-DTPA on Health and Welfare of the African Catfish Clarias gariepinus (Burchell, 1822)

Fingerlings (0.23 g) and juveniles (267.04 g) of African catfish (Clarias gariepinus) were reared for 32 days under experimental aquarium conditions and were exposed to either 0.75 mg/L or 3.0 mg/L diethylenetriaminepentaacetic acid-iron(II) (Fe-DTPA) and 3.0 mg/L or 12.0 mg/L Fe-DTPA in the water, respectively. These treatment groups were compared to a control group without additional Fe-DTPA. The growth, mortality, ethological indicators (activity, agonistic interactions, air-breathing), leukocyte distribution, histopathological changes in liver and gills, and genetic biomarkers were evaluated for each group. While the growth, mortality, and behavior were not significantly different between the groups, the lymphocyte count in the fish's blood increased significantly in all groups during the course of the experiment, but independently from the treatments. A similar trend (p > 0.05) was observed in monocytes. The number of granulocytes decreased significantly, but independently from the treatments. These changes indicated the possibility of an ongoing immune response in the fish from all treatments that might be caused by the increasing aggressive behavior of the fish. However, the Fe-DTPA treatments did not cause a notable suppression or enhancement of the immune reactions. Fe3+ accumulations in liver tissues were detected at the tested concentrations, and further changes occurred in the cells of the gills. Gene-expression biochips were used to simultaneously quantify the transcript levels of 34 genes associated with iron metabolism and stress physiology in head kidney samples. The obtained gene-expression profiles did not reveal any significant differences across either the different treatments or the time points. The results indicate that Fe-DTPA supplementation in the tested concentrations can be considered relatively harmless for the health and welfare of African catfish.