Histological and Histochemical Investigations of the Kidneys of Some Water Birds With Different Diets

"Avian species differ in their environments and lifestyles, including domestic, marine, wild, and carnivorous types. Each bird's unique diet influences the kidney to carry out distinct and specialized functions. This study aims to explore and compare the anatomical, histological, and histochemical features of the kidneys in aquatic birds with varying feeding behaviors: the Northern Shoveler (Spatula clypeata) and Green-winged Teal ( Anas crecca ) from the Anatidae family, and the Pied Kingfisher ( Ceryle rudis ) from the Alcedinidae family. The kidneys were dissected from the synsacral fossa and fixed in 10% neutral buffer formalin. Tissue samples were processed using the paraffin-embedding technique and stained with H&E, Periodic acid-Schiff (PAS), Alcian blue (AB), AB/PAS, and mercury bromophenol blue. Histological examination revealed no significant structural differences in the kidneys among the studied species. A thin basement membrane supported the endothelial cells of the glomerular capillary tufts. The lining epithelial cells of all segments of the nephrons and the brush border of the proximal convoluted tubule showed a negative reaction with Alcian blue stain. Whereas they exhibited a positive reaction with PAS stain. The distal convoluted tubules and the luminal surfaces of the collecting ducts showed a strong positive reaction with Alcian blue when combined with PAS. The proximal convoluted tubules showed a positive reaction with the mercury bromophenol blue stain, indicating the formation of albumin spheres. Histological and histochemical studies of the renal tissue across the three studied species revealed several interspecies similarities and some intra-species variations with other avian species.