Microanatomy and ultrastructure of kidney interstitial cells and nephron in brown trout (Salmo trutta) at different stages of the life cycle

Abstract

The study focuses on the microanatomy and ultrastructural changes in the trunk kidney interstitium cells and nephrons in parr, smolt and spawning brown trout Salmo trutta Linnaeus, 1758 sampled in Luga River and Solka River, the tributaries of the Baltic Sea. Regardless of the type of cells or their structure, there were changes in their areas and the number and structure of organelles responsible for the transport, synthetic and energetic function of cells. Our data on the morphology of the nephron combined with data on its physiology suggest a fundamental change in kidney function during the parr-smolt transformation before migration; this could be a preadaptation for a successful life in saltwater where urine output is sharply reduced. Thus, detected structural features of the trunk kidney in brown trout S. trutta are cytological markers of the migration process. The numbers of lymphocytes, neutrophils and eosinophils with segmented nuclei increased from parr to smolts and then to spawners; only monotypic specific granules in neutrophils were found in smolts and spawners. Cells with radially arranged vesicles were described for the first time in brown trout S. trutta renal interstitium. Their origin has not yet been established. The shape of these cells changed from spherical to trihedral during fish maturation. All the above ultrastructural changes of renal interstitium cells could be considered cytological markers of cell maturity.

Histology and Ultrastructure of the Nephron and Kidney Interstitial Cells in the Atlantic Salmon (Salmo salar Linnaeus 1758) at Different Stages of Life Cycle

“…Several organs are involved in osmoregulation: the kidneys, gills, digestive tract, bladder, and endocrine glands [4]. Previous studies on Pseudetroplus maculatus (Bloch 1795), Alburnus escherichii Steindachner 1897, and Salmo trutta showed that adaptation to a hyperosmotic environment leads to a decrease in the diameter of Bowman's capsules, accompanied by a decrease in glomerular filtration rate, which indirectly indicates a reduction in the formation of primary urine [10,20,21]. Moreover, smolts can have epithelial cells that are smaller in area and height in their proximal tubules, which indicates a low glomerular filtration rate, a distinctive characteristic of marine fishes [8,9,22,23].…”

“…; endocytosis zone and a portion of the brush border in an adult S from the Barents Sea population (g). Cell units: urinary space (1), basement membrane (2), squamous epithelial cell (3), podocytes (4), cytopodia (5), endothelial cell (6), fenestra endothelial cells (7), capillary (8), nucleus (9), mitochondria (10), rough endoplasmic reticulum (11), gap junction (12), smooth endoplasmic reticulum (13), tubular endoplasmic reticulum (14), microfibrils (15), brush border microvilli (16), vesicle (17), secretory granules (18). The parietal layer of Bowman's capsule is formed by a basement membrane lined with squamous epithelial cells with centrally located nuclei.…”

“…Migrating salmon exhibit high adaptive capacity during these habitat shifts [3][4][5][6][7]. The vast majority of studies on salmon migration are related to physiological changes in the osmoregulatory system, with only a few studies on the ultrastructural changes in the nephron [4,[8][9][10].…”

“…Previously, changes in the essential kidney excretory units, depending on sex and season, were registered in adults of Salmo trutta f. fario Linnaeus 1758 at a light-microscopic level using stereological methods [13]. Furthermore, some studies employed transmission-electron microscopy to describe the histology and ultrastructure of the trunk kidneys in brown trout Salmo trutta [10] and the proximal tubule of the nephron in the Pacific salmon [9,14] at the freshwater ontogenetic stages. To the best of our knowledge, there are no studies covering the structural changes of all the principal mesonephros functional units in salmon in both the freshwater and the seawater period of their life cycle.…”

New Data on Nephron Microanatomy and Ultrastructure of Senegal Bichir (Polypterus senegalus)

“…It is known that the outer diameter of the tubules depends both on the lumen of the tubules and on the height of the epitheliocytes that form the tubules. The height of nephron epithelial cells increases in the following order: P. senegalus —freshwater bony fish— C. punctatus , Coregonus migratorius—lungfish P. dolloi —amphibian Bufo bufo [ 15 , 17 , 18 , 19 ].…”