Ontogenic development of digestive accessory glands in larval and juvenile Vimba bream, Vimba vimba (Pallas, 1814)

Abstract

The current research investigated histological development and histochemistry of digestive accessory glands of Vimba vimba from hatching through 60th day after hatching (DAH). The samples were randomly taken from day 1 (hatching) until the yolksac was absorbed (day 7) and during following day, on a daily basis, then with 2, 5, and 10 days intervals until 60 DAH. Histological procedures including fixation, tissue processing, sectioning‌, general staining such as Hematoxiline-Eosine and specific staining such as Periodic-Acid Schiff (PAS), were carried out . A primordial liver was observed at 1 DAH in the ventral region of the yolksac. The pancreas was observed at 2 DAH, and gall bladder and bile duct were developed at 4-5 DAH. At the same time when larvae were growing, digestive accessory glands continued differentiation and, at 5 DAH, hepatocytes of liver with eosinophilic cytoplasm and basophilic granules showed regular shape around Sinusoids. Coinciding with the liver development, sinusoids developed as well and hepatic cells increased in size. Sinusoids store large amount of blood to provide the necessary conditions for liver metabolism. Also, at this stage, eosinophilic zymogen granules of exocrine portion of pancreas were observed. Secretory activity of digestive accessory glands began with the emergence of PAS positive cells followed by secretion of neutral mucopolysaccharides and glycogen compounds in liver cells of larvae at 4 DAH and pancreatic cells of larvae at 4-7 DAH. In general, the results of this study can be used to identify the factors limiting larval growth, reducing casualties during exogenous feeding, and even considering a proper diet for digestive system.