Morphological and histochemical characterisation of the mucosa of the digestive tract in matrinxã Brycon amazonicus (Teleostei: Characiformes)

Abstract

This study describes anatomical, histological and histochemical features of the digestive tract mucosal layer of the matrinxã Brycon amazonicus, an omnivorous freshwater fish endemic from the Amazon basin. This species presents short thick oesophagus with longitudinal folds, that allow the passage of large food items. The mucosa is lined with a stratified secretory epithelium rich in goblet cells that secrete neutral and acid mucins. The two mucin types provide different viscosity in anterior and posterior oesophagus related to the protective and lubricant functions, respectively. The stomach is a highly distensible Y‐shaped saccular organ. Here, it is proposed that this anatomical shape plays an essential role in food storage when food availability is abundant. The stomach mucosa is composed of epithelial cells with intense neutral mucin secretion to protects against gastric juice. The intestine is slightly coiled and presents internally a complex pattern of transversal folds that increases the absorption surface and the retention time of food. Goblet cells in the intestine secrete acid and neutral mucins that lubricate the epithelium and aid in the digestive processes. In the rectum, an increase in goblet cells population occurs that may be related to better lubrication.

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

“…Their histological structure resembles to the intestine and more specifically to its anterior part according to the mucosa organization and mucus composition. In that latter regard, our results are similar to previous studies describing acidic mucins with a majority of sialomucin for the goblet cells in the intestine although with smaller amounts of sulfomucin (e.g., Kalhoro et al, 2019 ; Vidal et al, 2020 ). However, some exception are noticed for the pyloric caeca and anterior intestine in P. orbicularis in which acidic mucus is present at the base of the folds and become progressively neutral at the top of the folds, with intermediate mixed mucus.…”

“…However, according to the literature the majority of protein intake (80%) and lipid absorption take place in the anterior intestine whereas macromolecules absorption main site is the posterior intestine for various fish species ( Wilson & Castro, 2010 ; Ray & Ringø, 2014 ). Finally, the rectum is distinguished from the rest of the GIT by a thickening of both muscle layers (particularly the circular layer), a reduction of the lumen size and the fold height as described in most of the teleost (e.g., Hellberg & Bjerkas, 2000 ; Vidal et al, 2020 ). These elements together with the presence of goblet cells are most probably associated with the defecation in this species.…”

“…Although the orbicular batfish GIT is highly convoluted compared to other teleost species, its organization is similar (e.g., ( Løkka et al, 2013 ; Alix et al, 2017 ; Kalhoro et al, 2019 ; Vidal et al, 2020 )). It presents a foregut (esophagus and stomach), a midgut (intestine) and finally, a short hindgut (rectum), separated by several identified junctions and valve.…”

“…It presents a foregut (esophagus and stomach), a midgut (intestine) and finally, a short hindgut (rectum), separated by several identified junctions and valve. The transition between the esophagus and the stomach even if not well defined, can be identified using the color of the organ, muscle layers and the presence or absence of mucous subepithelial glands ( Hellberg & Bjerkas, 2000 ; Ray & Ringø, 2014 ; Vidal et al, 2020 ). 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 ).…”

“…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 ).…”