Acetylcholinesterase,glutathione and hepatosomatic index as potential biomarkers of sewage pollution and depuration in fish

The current study was designed to validate the biomarkers of sewage pollution in Mozambique Tilapia (Tilapia mossambica, Peters) reared in sewage treatment plant (STP) effluent in Ras Al Khaimah, United Arab Emerates, before and following depuration/detoxification. Cellular biomarkers, cholinesterase activity using acetylcholine as a substrate (acetylcholinesterase AChE) and reduced glutathione (GSH) and hepatosomatic index (HSI) were investigated in fresh water fish, Tilapia, raised in a fish farm (Group I/Clean, as Control), treated sewage water/TSW (Group II/Sewage) and thereafter exposed to fresh water in an aquarium for 6 weeks (Group III/Depurated) for depuration. The results showed significantly lower levels of AChE activities in liver (26% p < 0.01) and muscle (30% p < 0.01) of the fish reared in the STP water (Group II/Sewage) as compared to those recorded in the fish from fish farm (Group I/Clean). The depressed AChE level was fully restored in the muscle but partially in the liver after depuration (Group III/Depurated). In contrast, GSH levels were significantly raised in both liver (1.3-fold p < 0.01) and muscle (4-fold) of Group II fish as compared to Group I (control) fish raised in fish farm and following depuration in fresh water (Group III/Depurated) elevated GSH level in liver restored to control values, while remained unchanged in muscle. The average hepatosomatic index (HSI = weight of liver × 100/total fish weight), an indicator of hepatomegaly, in the Group II fish reared in TSW was also significantly higher than that in the reference Group I fish, but decreased to control level in Group III fish following depuration. This study suggests the importance of cellular biomarkers, AChE, GSH and hepatosomatic index in monitoring the impact of sewage water pollution on fish caused by a complex mixture of chemico-biological contaminants and its mitigation following depuration, an effective mean of fish detoxification.