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.

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The karyotype and constitutive heterochromatin pattern of the white stork Ciconia ciconia samples obtained from Manzala lake, Dimiaat, Egypt was described. Somatic cells of Ciconia ciconia samples have diploid number 2n= 68 chromosomes. Out of 68 chromosomes, 11 pairs including sex chromosomes were macrochromosomes and the remaining pairs were microchromosomes. Of the 11 macrochromosome pairs, no.1, 2, 4 and 5 were submetacentric and pairs no. 6, 7 and 8 were described as metacentric. In addition, the autosome pair no.3 was subtelocentric, while autosome pair no.9 was acrocentric. Also, the sex chromosome Z represents the fourth one in size and it was classified as submetacentric while, W chromosome appeared as medium size and was acrocentric. Furthermore, C-banding pattern (constitutive heterochromatin) revealed variation in their sizes and occurrence between macrochromosomes. Pairs no. 7 and 8 of autosomes exhibited unusual distribution of heterochromatin, where they appeared as entirely heterochromatic. This may be related to the origin of sex chromosomes Z and W. However, there is no sufficient evidence illustrate the appearance of entirely heterochromatic autosomes. Therefore, there is no available cytogenetic literature that describes the C-banding and karyotype of Ciconia Ciconia, so the results herein are important and may assist in cytogenetic study and evolutionary pattern of Ciconiiformes.

Mitotic chromosomal aberrations and DNA polymorphism (RAPD marker) were carried out on the Nile tilapia Oreochromis niloticus collected from five sites in Minia governorate, Egypt to test their applicability as biomonitors for heavy metal contaminants of water. The diploid chromosome number of O. niloticus population was 2 n = 44. Different types of chromosomal aberrations were recorded (e.g., deletion, ring, centromeric attenuation, end-to-end association, dicentric chromosome, stickiness chromosomes, endomitosis, fragments and chromatid gap). The chromosomal aberrations varied between O. niloticus population collected from five sites, and the most common type was ring (R) chromosomes. Samples obtained from Bahr Yousef and Irrigation drain exhibited the highest aberration frequency. The frequency of chromosomal aberration was positively correlated with the concentration of heavy metals where their concentration in the surface water of Irrigation drain and BahrYousef exceeded the limits defined by WHO as well as the concentration of Pb in muscles. The RAPD marker was also used to identify genetic variation among Nile tilapia samples collected from five different water sources. It created polymorphic and unique bands that can be used as genetic markers to track DNA variations. The dendrogram also revealed that exposure to heavy metal pollution causes gradual accumulation of variance, whereas areas subjected to environmental stress showed higher genetic variation and clustered together.

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