GALT is a primary lymphoid tissue and a part of mucosal lymphoid system. This system acts as the first line of immune defense against ingested pathogen. Numerous reports are explained that there are considerable differences in GALT structure and distribution among various fish species and also in different parts of the gut.

This study was made on the 20 normal, mature and same size Barbus sharpeyi. For microscopical study, the samples were taken from anterior, middle and posterior parts of intestinal bulb and main intestine with maximum 0.5 cm thickness. The samples were fixed in Bouin's fixative and the serial sections were made on by routine paraffin embedding and stained by H&E and PAS.

The results showed that the lymphoid tissue is present in two different types and in two areas of intestinal bulb and main intestine of Barbus sharpeyi. In the first type, the lymphoid cells were scattered in the mucosal epithelium and in the second type, the lymphoid cells were present as an aggregated cord-like structure in the lamina propria or as diffuse type in the submucosa. The majority of lymphoid cells were lymphocyte and lymphoblast with a few macrophages and plasma cells. The most interesting finding was the lack of lymphoid follicles and payer^'s patches in different parts of the Barbus sharpeyi alimentary canal. Histometrical results showed that there are a significant difference in the density and distribution of intraepithelial lymphocyte in different parts of intestinal bulb and main intestine (P<0.05) but there were not seen any significant difference between male and female fish (P>0.05). The most intraepithelial cells were located in anterior part of intestinal bulb and in posterior part of main intestine in both sexes. The results suggest that location, shape and density of lymphoid cells of GALT in Barbus sharpeyi have considerable species differences.