Experiments on hybrid red tilapia Oreochromis sp. were conducted to assess histopathological effects induced in gill tissues of 96 h exposure to waterborne lead (5.5 mg/L). These tissues were investigated by light and scanning electron microscopy. Results showed that structural design of gill tissues was noticeably disrupted. Major symptoms were changes of epithelial cells, fusion in adjacent secondary lamellae, hypertrophy and hyperplasia of chloride cells and coagulate necrosis in pavement cells with disappearance of its microridges. Electron microscopic X-ray microanalysis of fish gills exposed to sublethal lead revealed that lead accumulated on the surface of the gill lamella. This study confirmed that lead exposure incited a difference of histological impairment in fish, supporting environmental watch over aquatic systems when polluted by lead.

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The present study was conducted to assess the water quality and bioaccumulation of heavy metals (Cd, Cu, Pb, and Zn) in tissues of the tilapia fish (Oreochromis niloticus) and shrimp (Metapenaeus affinis), which were caught from Shatt al-Arab river near Al-Najibiya power plant in Basrah, Iraq during Mar 2018 -Feb 2019. Aquatic samples consisted of raw water from the river, drainage channel water, and demi water from the inside electric power plant. 10 parameters including the electrical conductivity, total dissolved solids, total suspended solids, the concentration of hydrogen ions, calcium, magnesium, chloride, sulphate, phosphate, and temperature were examined. The results designated that a deterioration in the water quality of Shatt al-Arab was observed during the hot months, especially in the summer season of 2018. The conductivity rates were higher than the permissible limits compared to demi industrial water. Occurrence of heavy element concentrations of Cd, and Pb were in slightly higher average level in water samples collected from river raw water (0.62 and 0.14 mg/l) and drainage chanal water (0.17 and 0.15 mg/l) respectively. The concentration average of the heavy metals in the investigated parts (muscle, gill, and liver) of the studied fish could be found with significant variation among examined tissues. The current study concluded that the metal concentrations in muscles of the tilapia fish and the edible parts from studied shrimps were within the limits permitted for human consumption.

The current study was intended to investigate the responses of freshwater fish Carassius gibelio as an in vivo model by measuring the activity of the enzyme of the liver. Fish exposed to sub-lethal toxicities due to zinc metal and crude oil. Fish were treated to 0.6 and 1.2 mg/l for zinc ions as well as 500 and 2500 mg/l for crude oil during 96h, and the alterations in serum enzyme activities were determined aspartate aminotransferase (AST) and alanine aminotransferase (ALT). Zinc toxicity elevated activity level in hepatic enzymes in a significant way (P < 0.05). The present study appeared the slightly augmented levels of AST in the serum of C. gibelio when exposed to sub-lethal Zinc concentration while the serum ALT activity increased in response to the high level of Zn exposure when compared to control after (96 h). In addition, acute concentrations of crude oil after 96 h exposure can cause harmful effects on Carassius gibelio including the induction of (AST). However, not effecting found (ALT). We are concluded that changes in the activity of the enzyme can be considered as a pointer of the pollution impact in fish.

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