Zoological Studies

Vol. 51 No. 7, 2012

Effects of Sublethal and Lethal Copper Concentrations on the Gill Epithelium Ultrastructure of Nile Tilapia, Oreochromis niloticus

Sandra Mariza Monteiro1,*, Elsa Oliveira2, António Fontaínhas-Fernandes1, and Mário Sousa2,3

1Department of Biology and Environment and Center for Research and Technology for Agro-Environmental and Biological Sciences, University of Trás-os-Montes and Alto Douro, Apartado 1013, Vila Real 5001-801, Portugal
2Lab Cell Biology, Institute of Biomedical Sciences Abel Salazar (ICBAS), University of Porto, Porto 4099-003, Portugal
3Center for Reproductive Genetics Alberto Barros, Porto 4100-009, Portugal

Sandra Mariza Monteiro, Elsa Oliveira, António Fontaínhas-Fernandes, and Mário Sousa (2012) Histopathology is currently being used as a screening method to detect copper toxicity in fish.  However, a knowledge gap exists regarding copper’s effects on the gill epithelial ultrastructure.  To fill in this gap, Nile tilapia Oreochromis niloticus were acutely exposed to sublethal and lethal waterborne copper concentrations.  Results showed that in the basal region of gill lamellae, a sublethal concentration caused edema, stretching of pillar cells (PLCs), and the disappearance of pericytes (PCTs), whereas in the apical region PLCs remained intact, and PCTs and pavement cells (PVCs) were activated.  In the filament epithelium, PVCs showed structural signs of high functional activity, while mitochondrion-rich and mucous cells were degenerated.  In the deep filament region, there were edema, loss of neuroepithelial cells, proliferation of undifferentiated cells (UDCs), and transformation of leukocyte-like cells into macrophages.  Acclimation was characterized by vasodilatation of the entire lamellar axis and a decrease in the filament epithelial thickness.  The protruding lamellae showed PCT proliferation, whereas the superficial filament epithelium became denser due to UDC attachment.  All fish exposed to the lethal dose died within 24 h.  Gills showed vasodilatation and edema that had lifted the PVCs, and necrosis was evident.  In conclusion, our findings contribute to clarification of gill epithelial cell dynamics, and also revealed that apical and basal regions of the lamellae showed different responses, with the apical region exhibiting higher resistance to the toxic actions of copper.  Also, superficial and deep regions of the filament epithelium showed dissimilar responses to copper, with the deep epithelium playing important roles in regeneration and protection.

Key words: Teleostei, Branchial epithelium, Ultrastructure, Copper, Acute toxicity.

*Correspondence: Tel: 351-259-350108.  Fax: 351-259-350266.    E-mail:smonteir@utad.pt