Juvenile tilapia (Oreochromis mossambicus) strive to maintain physiological functions after waterborne copper exposure

Juvenile tilapia were acutely exposed to 0.2 and 2 mg/L Cu²⁺ for up to 144 h. The Na⁺-K⁺-ATPase (NKA)-specific activity in the gills of tilapia exposed to 0.2 mg/L Cu²⁺ significantly decreased over 48-72 h and was restored to the control level after 96 h, but was again depressed during 120-144 h. The whole-body Cl^- levels significantly decreased after 48 h, but recovered shortly afterwards and continued to do so until 144 h with 0.2 mg/L Cu exposure. During 48-72 h, the numbers of the wavy-convex type of mitochondria-rich (MR) cells appeared to significantly increase and the cortisol content also significantly increased. Changes in MR cell morphology might be necessary in order to enhance Cl ^- uptake, and this might be related to changes in cortisol levels. Whole-body Na⁺ concentrations had significantly decreased by 72 h, but recovered during 96-144 h. Whole-body Cu²⁺ concentrations also significantly increased compared to the initial concentration during 72-144 h of Cu exposure. All measured parameters (NKA activity, Na⁺ concentration, and MR cell numbers) significantly decreased in fish exposed to 2 mg/L Cu, and no recovery was observed. These data demonstrate that juvenile tilapia strived to maintain physiological functions after exposure to sub-lethal concentrations of Cu.