Changes in humoral and cell-mediated immune responses and in skin and respiratory surfaces of catfish, Saccobranchus fossilis, following copper exposure

Abstract

Immunologic responses and stereoscan analysis of the skin and gill surfaces were performed in the air-breathing catfish, Saccobranchus fossilis (Bloch) following sublethal exposure to copper. At 0.056, 0.1, and 0.32 mg/liter of Cu, a dose-dependent decrease in red and white blood cell counts, hemoglobin content, and packed cell volume values were observed at the end of experiment, i.e., 28 days. Fish exposed to Cu concentrations had lower antibody titer values, reduced numbers of splenic and kidney plaque-forming cells, and higher counts of splenic lymphocytes when compared to the control group. Cellular immune responses were evaluated by the rejection of eye allografts. Fish exposed to 0.32 mg/liter for 28 days showed 2–3 days delay in the eye-allograft rejection. Reduced phagocytic activity against sheep red blood cells was observed in Cu-treated fish. Exposure to 0.32 mg/liter of Cu for 7 days causes surface architectural abnormalities in the arrangement of microvilli on the surface of superficial epidermal cells of the skin. Hypersecretion of mucous, loss of shape, size, and structural arrangement of epidermal cells, and mucous goblet cells were observed following Cu exposure. An increased number of active tubular dilated mucous cells were also noticed. Accumulation of mucous suggests a molecular interaction between mucous glycoproteins and toxic Cu ions. Fish exposed to 0.32 mg/liter for 7 days showed edema, fusion of secondary gill lamellae at many places, and degeneration of epithelial cells. Marked ultrastructural alterations in the arrangement of microridges and intervening grooves of gill lamellae were noted. It is suggested that these degenerative changes in gill lamellae are responsible for respiratory and osmoregulatory dysfunction.