Histological structure of the intestine and pyloric caeca of the green sunfish, Lepomis cyanellus Rafinesque

A histological study was made of the intestine and pyloric caeca of green sunfish, Lepomis cyanellus (Centrarchidae). The intestinal and caecal walls are histologically very similar, consisting of a mucosa (epithelial layer), submucosa (lamina propria and stratum compactum), muscularis (circular and longitudinal layers) and the serosa. Cellular constituents of the mucosal layer include absorptive, columnar epithelial cells, mucous‐secreting goblet cells, and various leucocytes, the majority of which are lymphocytes. Other than relative size and the entrance of the bile duct at the base of the first caecum, no difference was found among caeca. When fish were nutritionally stressed, a greater variety and number of leucocytes and shifts in the numbers of lymphocytes and goblet cells of the mucosal layer were the only observable effects.