| Summary: | The main goal of this work was to improve the understanding of the intestinal pathophysiology induced by soya bean meal (SBM) in diets for Atlantic salmon. The effects brought about by dietary SBM, Inulin and oxytetracycline (OTC) were compared with fish meal (FM). This was carried out by analyzing fish organosomatic index of the gastro-intestinal tract including liver, nutritional plasma parameters, screening of gastro intestinal histology and the immunohistochemical detection of proliferating cell nuclear antigen (PCNA) of the distal intestine. Fish fed SBM diet had a significantly lower hepatosomatic index (HSI). A similar effect was seen with the inclusion of the OTC in the different diets. Fish fed the Inulin diet showed the highest distal intestinal somatic index (DISI), while fish fed the SBM diet showed the lowest DISI, compared to fish fed the FM diet. The low DISI of fish fed the SBM diets correspond with the morphological changes observed in the distal intestine. The response to OTC inclusion on total plasma protein differed depending on which diet the fish were eating. Immunohistochemical detection of PCNA in SBM fed fish indicated higher cell proliferation in the crypts of the distal intestine compared to the fish fed FM and Inulin diets. However, an estimate of total proliferating area of the distal intestine indicated that fish in the Inulin treatment had the largest total PCNA positive area, in agreement with the fact that these fish had highest DISI. Although exhibiting the lowest DISI, fish in the SBM treatment showed a similar total PCNA positive area along the distal intestinal folds to the Irrnlin treatment.
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