Growth differentiation factor 15 (GDF15),

Cytological, histopathological and sodium dodecyl sulphate polyacrylamide gel analyses were carried out on five populations of common Nile tilapia fish (Oreochromis niloticus) occurring in five sites – River Nile (reference site), Bahr Yusef canal, Ibrahimia canal, Irrigation drain and El Moheet drain of El Minia Province, Egypt – to evaluate the usability of Nile tilapia as a biomonitor for water heavy metal contaminants. Water surface samples were collected from the five sites, and lead (Pb) concentration was shown to surpass the limits defined by WHO. Ni and Cd levels were shown to be elevated in Ibrahimia canal samples. Moreover, the concentration of heavy metals in fish muscles collected from Bahr Yusef canal and El Moheet drain was the highest in comparison with those of the other water sites. Cytological examinations of blood smears showed not only a significant percentage of micronuclei in Irrigation drain population but also a significant percentage of binucleated cells in Ibrahimia canal and El Moheet drain populations. In addition, pathological alteration was observed in blood cells, especially in samples collected from Irrigation drain and El Moheet drain. Histopathological changes were strongly observed in the liver and the kidneys of El Moheet and Irrigation drain population. Moreover, total protein band pattern profiles showed extra bands in both Ibrahimia canal and Irrigation drain more than that recorded for the River Nile population. In conclusion, cyto‐histopathological and total protein band pattern results confirmed that O. niloticus responds sensitively to the excess of heavy metals present in the water.

INTRODUCTION Calcium carbonate precipitation is a natural process occurred in terrestrial and aquatic habitats, for instance, sands, coral reefs and shells (Barabesi et al., 2007; Kim et al., 2016). Bivalves shell ornamentation is mainly carried out by animal mantle with a potential role in shell assembly could be considered for some associated beta proteobacteria (Peharda et al., 2015). Some species members of the family Alcaligenaceae, belonging to the beta proteobacteria, are defined to induce calcium carbonate biomineralization (Daskalakis et al., 2013).

Morphological characteristics and electrophoretic protein patterns were considered in the present study to distinguish between two types of clinostomatid metacercariae from Oreochromis niloticus fish caught from the River Nile at El-Minia district, Egypt. Fifty-two specimens of randomly collected 120 examined fish were infected with both Euclinostomum ardeolae and Clinostomum phalacrocoracis metacercariae or either. Euclinostomum ardeolae metacercariae were embedded in Oreochromis niloticus tissues of the kidney as round to oval greyish black cysts giving the area around faint black color with a 15% prevalence rate of infection. Cyst was of variable size (3-4 mm) and thin completely tight wall. Metacercaria is aspinose pyriform in shaped, long 6.5 wide 2.3 mm, of blunt anterior end but the posterior one is nearly rounded. Clinostomum phalacrocoracis yellow to orange in color cysts were detected in the pharyngeal region and branchial chambers and the prevalence rate of infection was 39.16%. They varied in size (4-5.2 mm) with a thin transparent membrane full of yellowish fluid. The body of metacercaria was elongated, tongue-shaped, and slightly wider in gonadic region, long 16.4 wide 4.01mm. Electrophoretic protein profiles were resolved using one dimensional SDS-PAGE stained with Coomassie Brilliant Blue R-250 stain. Encysted and excysted Euclinostomum ardeolae metacercariae showed bands of 61 kDa, 29 kDa, 28 kDa, 15 kDa and 14 kDa, while Clinostomum phalacrocoracis encysted and excysted metacercariae revealed bands of 61 kDa, 54 kDa, 32 kDa, 31 kDa, 20 kDa, 17 kDa, 15 kDa and 14 kDa. Conclusively, biochemical findings are in concordance with morphological characterization confirming both metacercariae to be of two distant species.