Effects of diazinon on adaptation to sea-water by the endangered Persian sturgeon, Acipenser persicus, fingerlings

• Diazinon affected Na+/K+ ATPase activity, thyroid hormone levels and proliferation of chloride cells in sturgeon.
• Diazinon stimulated cortisol in Persian sturgeon fingerlings.
• Gill tissue damages occurred in diazinon-exposed fingerlings.
• Diazinon affected whole-body electrolyte levels in exposed fingerlings.

To replenish the depleting populations of sturgeon fishes especially Persian sturgeon, Acipenser persicus in the Caspian Sea, millions of Persian sturgeon fingerlings are farmed through artificial propagation and released into the Iranian river estuaries annually. Fish osmoregulation is a vital physiological process that can be affected during the release. Many Iranian river estuaries are under the influence of pesticides originating from farming activities that may affect osmoregulation. In this study, Persian sturgeon fingerlings were exposed to sublethal concentrations (0, 0.18, 0.54, 0.9 mg L−1) of diazinon for 96 h (short-term trial) and 12 days (long-term trial) in fresh water (FW) and then fish were exposed in brackish water (BW) for 24 h. After 96 h and 12 days of exposure in FW, the lower levels of plasma triidothyronine (T3), thyroxine (T4), Na+, Cl−, K+, gill Na+/K+- ATPase activity and number of chloride cells were observed in exposed fish (0.54 and 0.9 mg L−1 diazinon) compared to control group and 0.18 mg L−1 diazinon treatment. Also, higher levels of plasma cortisol (except 0.18 mg L−1 diazinon treatment in long-term trial) were observed in diazinon exposed fish compared to control group. However, gill Na+/K+-ATPase activity and the number of chloride cells were higher in fingerlings exposed to diazinon compared than control. When fish were exposed in BW for 24 h, the following changes occurred: (a) in short-term trial: increases in cortisol and Cl− levels (0.54 mg L−1 diazinon ), Na+ (0.9 mg L−1 diazinon ) and gill Na+/K+-ATPase activity (0.18 mg L−1 diazinon ). In control group, cortisol, T4, Na+, gill Na+/K+-ATPase activity and the number of chloride cells increased significantly. (b) In long-term trial: increases in K+ levels in fish exposed to 0.9 mg L−1 diazinon, Na+ in all diazinon concentrations and decreases in chloride cells number in fish exposed to 0.18 mg L−1 diazinon. In control group, significant increases were observed in cortisol, T3, Na+ and chloride cells number. Finally, gill showed many histopathological damages during exposure in FW and BW. Our results suggest that the contamination of river estuaries with diazinon may alter the osmoregulation ability of released Persian sturgeon fingerlings, which could lead to a failure in their restocking program in the Caspian Sea.

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