Study of pollution in Shatt AL-Arab River using histological alternations and some other biochemical parameters of gill in Nile tilapia (Oreochromis niloticus) as water quality biomarkers

This study aims to assess the pollution of Shatt AL-Arab River using histology and some other biochemical parameters of gill in Nile tilapia (Oreochromis niloticus) caught in winter 2021 at four locations as water pollution biomarkers.Some water quality parameters were determined in these sites, and the results showed that sites 2 and 3 are polluted at levels above the World Health Organization's guideline. The enzymatic and metabolism activity, histological status, and cytogenetic mutation over time in the gills were assessed. Biotransformation enzymes level showed total cytochrome p450 and Ethoxyresurofin–O–demethylase (EROD) activities are significantly increased in gills of tilapia in site 1, 2 and 3. The antioxidant enzymes activities were recorded significantly high in fish gills of catalase (CAT) and glutathione -S-transferase (GST) in polluted sites of 1, 2, and 3, while superoxide dismutase (SOD) were significantly higher only in site 3 compare with reference site of 4. The metallothionein-like protein (MTLP) was significantly higher in gills at site 3. Also, lipid peroxidation (LOP) and micronucleus analysis showed that sites 2 and 3 samples site the most affected. Gill tissue index was appeared severe alterations levels at sites 2 and 3, followed by site 1 with a relatively lower level of damage, while site 4 (reference one) showed minor or invisible changes in gill tissue. The histological alterations in the gills of Nile tilapia fish at sites 2 and 3 showed atrophy of cellular, hemorrhage, congestions, hyperplasia, and hypertrophy of the filament lamellae epithelium.