Effects of Cd, Zn and Cd+Zn combination on osmoregulation of tilapia (oreochromis niloticus)

The objectives of this study were to evaluate the effects of cadmium (Cd), zinc (Zn) and Cd+Zn combinations on serum osmolality and ions in Oreochromis niloticus. A total of 60 O. niloticus with five fi sh per tank and two tanks per group were used during this experiment. Group I was held in media without metal (as control) and other groups were exposed to 7.5 mg/L Zn, 15 mg/L Zn, 2.5 mg/L Cd, 7.5 mg/L Zn + 2.5 mg/L Cd and 15 mg/L Zn + 2.5 mg/L Cd for 7 days. The osmolalities of fish exposed to Cd, Zn and Cd+Zn combinations were higher than the control. Fish exposed to 2.5 mg/L Cd presented the highest level of Na⁺and Cl^-, and the lowest level of K⁺. This study shows that the osmotic and ionic regulatory impairment is more pronounced in fish exposed to Cd than in Zn and Cd+Zn combinations. This phenomenon indicates that Zn plays a prominent role in suppressing the toxic effect of Cd on O. niloticus.