Influence of enteric helminths on the distribution of intestinal endocrine cells belonging to the diffuse endocrine system in brown trout, Salmo trutta L.

The presence of intestinal helminths in the alimentary canal of brown trout Salmo trutta (L.) can alter the number of cells that synthesize modulatory peptides. Occurrence and density of endocrine cells responsible for the production of digestive peptides in the intestine of parasitized and uninfected specimens of brown trout were detected with immunohistochemical methods. A total of 167 brown trout were collected on several occasions from different tributaries of the River Brenta (northern Italy). One hundred nineteen (71.3%) specimens of S. trutta were infected with enteric helminths, respectively, 28 with the acanthocephalan Pomphorhynchus laevis (Müller, 1776) with intensity of infection ranging from 1 to 162 (18.57±30.79) worms per host and 67 fish were parasitized with the cestode Cyathocephalus truncatus (Pallas, 1781). Intensity of infection with tapeworm ranging from 1 to 85 (6.87±12.59) per fish. Moreover, in 24 fish, co-occurrence of both species of helminths was registered. The proximal (near the pyloric caeca) and the middle regions of the intestine were the most heavily parasitized. Immunohistochemical tests have shown a decrease in number of endocrine cells of the diffuse endocrine system (DES) positive to gastrin, cholecystokinin-8, bombesin and secretin antisera in the intestine of the infected trout. The number of endocrine cells immunoreactive to anti-glucagon serum did not show differences in the digestive tract of uninfected brown trout and in conspecifics parasitized with P. laevis. The density of cells containing glucagon-like material was low in the fish parasitized with C. truncatus. The present survey furnished compelling evidence that endoparasitic helminths induce alterations in the DES of infected S. trutta.