The digestive tube of Piaractus brachypomus: gross morphology, histology/histochemistry of the mucosal layer and the effects of parasitism by Neoechinorhynchus sp.

The objective of the present study was to describe the histology and histochemistry of the mucosal layer of the digestive tube of Piaractus brachypomus, and the histopathology associated with parasitism by Neoechinorhynchus sp. The digestive tube of P. brachypomus consists of three macroscopically distinct portions: short, rectilinear and elastic-walled ooesophagus, J-shaped siphon stomach and a long intestine with rectilinear and curved portions, defined by patterns of villi as foregut, midgut, and hindgut. Histological and histochemical differences were observed in the mucosal layers of the different digestive tube regions, such as intense production of neutral and acidic mucous substances in the pseudostratified mucosal epithelium of the oesophagus; positive periodic acid Schiff reagent (PAS)reactions at the apex of the columnar epithelial cells of the stomach and increased intensity of histochemical reactions in the hindgut region. Neoechinorhynchus sp. was present in 85.7% of specimens examined, with a mean intensity of 7.4 ± 6.2 (±) and abundance of 6.33. Good health of the fish indicated by high relative condition factor values ( Kn ) and occurrence of only mild to moderate alteration in the mucosal layer indicated that Neoechinorhynchus sp. exhibits low pathogenicity towards P. brachypomus hosts in farming environments, with low levels of infection.

Morphological and histochemical changes associated with massive infection by Neoechinorhynchus buttnerae (Acanthocephala: Neoechinorhynchidae) in the farmed freshwater fish Colossoma macropomum Cuvier, 1818 from the Amazon State, Brazil.

The study describes the morphological changes associated with parasitism by the intestinal acanthocephalan Neoechinorhynchus buttnerae in tambaqui juveniles Colossoma macropomum farmed in an excavated nursery, in Manaus (Amazon) in September 2013. After fish biometrics, analysis of macroscopic changes in morphology and counting of parasites, bowel fragments were fixed and submitted to histological and histochemical processing. All fish analyzed had acanthocephalans in the intestine; intestinal loops were milky white in color, with the presence of nodules with heavy parasitism. The changes in tissues that form the intestine varied according to the arrangement of the parasites: either free in the intestinal lumen or fixed by the proboscis on the organ wall. In the first case, the changes found were flaking, abrasion, compression, hypertrophy of goblet cells and disappearance of the villi on the mucosa, leukocytic cell infiltration in the submucosa, and muscle layer thickening. In the second case, in addition to these, other changes were observed as metaplasia in muscle tissue with its replacement by a loose connective tissue with severe leukocytic infiltration, edema in blood vessels, and necrotic foci. The histochemical analysis revealed that positive Alcian Blue mucosal cells (pH 2.5) were more expressive in parasitized intestines than in intestines not parasitized by N. buttnerae.