A Detailed Study of Rainbow Trout (Onchorhynchus mykiss) Intestine Revealed That Digestive and Absorptive Functions Are Not Linearly Distributed along Its Length

Abstract

To increase the sustainability of trout farming, the industry requires alternatives to fish-based meals that do not compromise animal health and growth performances. To develop new feeds, detailed knowledge of intestinal morphology and physiology is required. We performed histological, histochemical, immunohistochemical and morphometric analysis at typical time points of in vivo feeding trials (50, 150 and 500 g). Only minor changes occurred during growth whereas differences characterized two compartments, not linearly distributed along the intestine. The first included the pyloric caeca, the basal part of the complex folds and the villi of the distal intestine. This was characterized by a significantly smaller number of goblet cells with smaller mucus vacuoles, higher proliferation and higher apoptotic rate but a smaller extension of fully differentiated epithelial cells and by the presence of numerous pinocytotic vacuolization. The second compartment was formed by the proximal intestine and the apical part of the posterior intestine complex folds. Here we observed more abundant goblet cells with bigger vacuoles, low proliferation rate, few round apoptotic cells, a more extended area of fully differentiated cells and no pinocytotic vacuoles. Our results suggest that rainbow trout intestine is physiologically arranged to mingle digestive and absorptive functions along its length.

The 3D Pattern of the Rainbow Trout (Oncorhynchus mykiss) Enterocytes and Intestinal Stem Cells

“…The epithelium covering the apical part of the complex folds of the second segment presented abundant and actively secreting goblet cells and no pinocytotic vacuoles in the first segment of the mid-intestine, whereas the pyloric caeca and the basal part of the complex folds in the rest of second segment of the mid-intestine were lined with an epithelium characterized by few deflated goblet cells and high pinocytotic vacuolization. Moreover, these two intersected districts showed distinct turnover rates: the first segment of the mid-intestine and the apical part of the complex folds were characterized by low proliferation and extensive differentiation, while the contrary occurred in the pyloric caeca, the basal part of the complex folds, and the rest of the second segment of the mid-intestine [5].…”

“…Fish represent the largest group of vertebrates, including almost 21,000 species, more than all other vertebrates combined; they are characterized by a wide variety of anatomical and physiological differences [4]. We recently examined in detail the intestinal structure of rainbow trout (RT; Oncorhynchus mykiss) [5], a member of the Salmonidae family, one of the most successful groups in aquaculture by virtue of its adaptability to a wide range of farming conditions [6]. Following the nomenclature proposed by Bjørgen et al [7] for the Atlantic salmon (Salmo salar), along the craniocaudal axis of the intestine, we first meet the pyloric caeca, over 50 hollow tubes that branch off the first segment of the mid-intestine, to increase its absorptive surface.…”

“…Throughout the length of the whole intestine, the mucosa raises in large folds, and, in the second segment, some of them are up to three times higher with smaller secondary folds branching out along their length. For their peculiar structure, these are known as complex folds [5,9].…”

“…We previously described a peculiar distribution pattern of the different cell populations along rainbow trout intestinal mucosa [5]. The epithelium covering the apical part of the complex folds of the second segment presented abundant and actively secreting goblet cells and no pinocytotic vacuoles in the first segment of the mid-intestine, whereas the pyloric caeca and the basal part of the complex folds in the rest of second segment of the mid-intestine were lined with an epithelium characterized by few deflated goblet cells and high pinocytotic vacuolization.…”

Description of the unusual digestive tract ofPlatax orbicularisand the potential impact ofTenacibaculum maritimuminfection

“…The stomach displays a siphonal (J or U) shape which is the most common type among fish (e.g., Eastman & DeVries, 1997 ; Løkka et al, 2013 ; Kalhoro et al, 2018 ). P. orbicularis has pyloric caeca as approximately 60% of teleosts (e.g., Pedersen & Falk-Petersen, 1992 ; Løkka et al, 2013 ; Aguilar-Medrano, Kobelkowsky & Balart, 2015 ; Alix et al, 2017 ; Kalhoro et al, 2018 ; Kalhoro et al, 2019 ; Vidal et al, 2020 ; Verdile et al, 2020 ). These blind-ended ducts are probably involved in the surface area increase for absorption and digestion ( Pedersen & Falk-Petersen, 1992 ; Ray & Ringø, 2014 ).…”