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| Stannius corpuscles (SC) are unique endocrine gland in the kidney of bony fish. It plays an important role in regulating calcium haemostasis via secretion of hypocalcine (stanniocalcin) hormone. The structure of Stannius corpuscles has been clarified in several fish species; however, little was elucidated concerning that in African catfish (Clarias gariepinus). Therefore, the aim of the current study is to reveal the structural characteristics of SC in African catfish (Clarias gariepinus) among both sexes. Histological and ultrastructural examinations of SC were revealed among both sexes. The SC were paired, oval white colored bodies embedded in the trunk area of posterior kidneys. Histologically, the SC were surrounded by thin connective tissue (C.T) capsule from which many septa were extended dividing the glands into incomplete lobules. The parenchymal cells consist of two types; one with intensely eosinophilic cytoplasm and the other were weakly stained. Interestingly, the proportion of cells was varied among male and female. The female showed significant higher percentage of lightly eosinophilic cells than the intensely stained cells. On the other hand, the predominant cell type in male was the intensely stained one. Transmission electron microscopic observations revealed the presence of two types of cells; predominant type I (electron dense and electron lucent cells) and type II. The former showed more secretory granules than the later. In conclusion, our results revealed sexual differences in the proportion of cells and suggested that the type I could be responsible for hypocalcine hormone secretion. However, further investigations are required to reveal the structure of SC among different seasons.

The aim of this research work was to study the histological structure of the pancreatic acini by transmission electron microscope in two avian species, duck and pigeon. The specimens were collected and processed for electron microscopic study. The results showed that the acini of the two avian species were two types; the first one was an electron dense and the second one an electron lucent. The light acinar cells were larger in size than the dark cells. These cells contained centrally located ovoid nuclei with prominent nucleoli and abundant euchromatin. The cytoplasm was electron lucent, with many rough endoplasmic reticulum, polymorphic mitochondria. Numerous zymogen granules were distributed in the basal part and around the nucleus, so these cells considered active cells. The dark acinar cells were characterized by an electron dense cytoplasm. The most prominent cell organelle in these cells were the zymogen granules that appeared in different sizes while other organelles as mitochondria, and rough endoplasmic reticulum were inconspicuous or few, so these cells were considered as inactive cells. The nucleus with indented nuclear membrane located centrally with prominent nucleoli and abundant heterochromatin. Prominent intercellular spaces between the individual acinar cells, as well as well‐developed basement membrane separating the electron dense cells and the lumen contained the secretion between acinar cells. It could be concluded that the acinar cells in ducks and pigeons were divided into two types, that is, light and dark acinar cells which mainly attributed to the activity of these cells.

Background:The fish pancreas has been reported to be composed of two portions: compact and disseminated. However, little has been elucidated in catfish. The present study describes a unique localization of the disseminated pancreas in African catfish. Methods:The sections were obtained and used for either routine histological examination following staining with haematoxylin and eosin (H & E), periodic acid-Schiff's, or were subjected to immunohistochemical staining for detection of both insulinproducing β cells and glucagon-producing alpha cells.Results: Our investigation showed that the pancreas of catfish consisted of both compact and disseminated portions. The compact pancreas was embedded in the mesenteric adipose tissue between the spleen, stomach and liver. However, the disseminated one showed unique localization in the tunica adventitia of the middle portion of the oesophagus. The pancreas consisted of two portions, exocrine and endocrine. Furthermore, in both types of pancreas, the female showed a significantly higher ratio for the endocrine islet area/pancreatic tissue area than that of the male and also a significantly higher ratio for both insulin-and glucagon-positive area/islet area in the female pancreas (compact and disseminated) than that of the male. In conclusion:The present study provides evidence on a unique localization of the disseminated pancreas in the oesophagus of catfish. Furthermore, we revealed sexrelated difference in the endocrine portion in both pancreatic tissues with more development in the female. The study suggests that sex hormones could be contributed to such sexual dimorphism. However, further investigation is required to compare the degree of development during the spawning and resting seasons. K E Y W O R D Sglucagon-secreting alpha cells, insulin-secreting beta cells, islets of Langerhans, oesophagus, pancreas | 595 KARKIT eT Al.