Objective: Recognizing thc morphologic and microscopic structurcs of some parts of the G.l tract which have the most important absorptive role in relation with feeding and growth of the sturgeons. Design: Descriptive study.
Animals: A total number of six adult Russian sturgeons freshly prepared from Caspian sea.
Procedure: After removing the posterior parts of G.l tract, they were immediately fixed in %l0 buffered formalin and transported to the laboratory. Routine procedures of histology were made and the paraffin sections of 5 micron were stained by Hematoxylin and Eosin. Results: The large or spiral intestine was characterized with particular spiral valves. They were lined with a pseudostratified epithelium encircled by a connective tissue layer and strands of smooth muscle and some lymphatic nodules. A similar epithelium was present in spiral intestine’s mucosa. In lamina propria and submucosa were some simple tubular and many large branched sacular glands with the same epithelium. Numerous secretory and granular cells were seen in this epithelium. Rectum had a pseudostratilied epithelium with brush borders and numerous goblet cells. The large glands of the previous parts were absent. The epithelium gradually changed into stratified squamous toward the anus at the end of the canal. Conclusion: Considering the presence of many goblet and secretory cells in the mucosal epithelium of these parts and also spiral valves, in some species it has been shown that the enzyme concentrations and protein levels in these parts were higher. So it is concluded that especially the spiral intestine to be the principal site of absorption in sturgeons, this study also showed that, in this species due to presence of a highly complex mucosal structures, large absorptive areas have been provided, which is correspondent with the route of
their feeding. J. Fac. Vet. Med. Univ Tehran. 58, 1: 45-48, 2003.