Histological Changes in the Liver and Intestine of Nile Tilapia, Oreochromis niloticus, Exposed to Sublethal Concentrations of Cadmium

Cadmium (Cd) is one of the most harmful heavy metal pollutants in aquatic environments. Fingerlings of Nile tilapia, Oreochromis niloticus, were exposed to sublethal concentrations (10, 20 and 30% of the 96-h LC50) CdCl2 which caused significant changes in concentration dependent manner in the hepatic and ileal tissues. The hepatic tissue lost its characteristic architecture, with increased vacoulations in hepatocytes. In addition, abundant eythrocytic infiltration was observed in the 10% of LC50 group and clearly increased in the 20% of LC50 group. Increase of hemorrhage, vacuolation in hepatocytes and infiltration of sinusoids with leukocytes were observed in the 30% of LC50 group. The intestinal tissue in the treated groups was characterized by increased degenerated nuclei and apoptosis in crypts of Lieberkuhn, in addition to abnormally dilated lamina propria infiltrated with a large number of inflammatory leukocytes and disturbance of the longitudinal muscularis. Goblet cells increased in all treated groups, indicating a defense mechanism against the severe pathological changes induced. In conclusion, severe damage to the hepatic and intestinal tissues of the Nile tilapia was observed upon contamination of the fish environment with CdCl2.