Changes in the neuromodulators of the diffuse endocrine system of the alimentary canal of farmed rainbow trout, Oncorhynchus mykiss (Walbaum), naturally infected with Eubothrium crassum (Cestoda)

Abstract

A histopathological and immunohistochemical study on the intestines of 45 specimens of farmed rainbow trout, Oncorhynchus mykiss (Walbaum), from Loch Awe, Scotland, revealed a number of cellular deviations in individuals naturally infected with the pseudophyllidean cestode Eubothrium crassum (Bloch, 1779). Twenty‐five individuals (55.5%) were infected with an average worm burden of 18.84 ± 4.06 (mean ± SE) cestodes per host (range, 2–80 worms; total 471 worms). The cestodes, measuring an average 8.23 ± 1.10 cm (mean ± SE; range, 5.3–13.0 cm) in length, were found attached by their scolices to the mucosal lining of the distal portion of the pyloric caeca. Within the caeca, the strobila evoked a mild catarrhal enteritis, namely an enhanced mucus production with epithelial cellular desquamation, a leucocytic infiltration of the lamina propria‐submucosa and vacuolization of the intestinal epithelial cells. Eosinophilic granular cells of the stratum granulosum exhibited granular depletion, while within the catarrh, the presence of a high number of rodlet cells was noticed. Immunohistochemically, the occurrence of E. crassum caused a significant reduction in the number of bombesin‐, gastrin‐releasing peptide and glucagon‐like immunoreactive endocrine cells, but an increase in the relative densities of endocrine cells containing cholecystokinin‐8‐ and gastrin‐like substances. There were, however, no significant differences in the number of endocrine cells that were immunoreactive to secretin, neuropeptide Y and peptide histidine–isoleucine antisera in the digestive tracts of either the infected or non‐infected O. mykiss .

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