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

The current study investigated histological development and histochemistry of digestive accessory glands of Vimba bream Vimba vimba from hatching through 60th day after hatching (DAH). The samples were randomly taken from day 1 (hatching) until the full absorption of the yolk sac at day 7 and the day after that, then with 2, 5, and 10 days intervals until 60 DAH. The development of the digestive accessory glands was followed histologically using light microscopy after Haematoxylin-Eosin and Periodic-Acid Schiff (PAS) staining. A primordial liver was observed at 1 DAH in the ventral region of the yolk sac, pancreas at 2 DAH, 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. 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. The results of this study can be effective in identifying growth limiting factors in breeding larvae, reducing casualties during exogenous feeding, and even developing a proper diet for its digestive system.