Análises morfológicas, morfométricas e histoquímicas do tubo digestivo de Brycon Amazonicus (Spix & Agassiz, 1829)

Abstract

The digestive tube of fish has great morphological diversity and the study of its structural characteristics is important to understand the digestive physiology, facilitating the management of species. Thus, this work analyzed the anatomy, morphometry, histology and histochemistry of the digestive tract of Brycon amazonicus, a species widely used in fish farming due to the quality of meat and sportsmanship. Eighteen adult specimens (36.2 cm ± 4.3 and 1.17 kg ± 0.34) were collected in fish farming and euthanized in benzocaine hydrochloride (CEUA Proc: 1005/2017). The samples were dissected, measured with a caliper and photo-documented using a digital camera and stereomicroscope. For histological and histochemical studies, tissue fragments were fixed in Bouin's solution and subjected to the routine of inclusion in historesin and paraffin. Subsequently, the histological materials were stained with hematoxylin and eosin, 1% toluidine blue, methanyl yellow, Masson's trichrome. The histochemical materials were stained with periodic acid from Schiff (PAS), Alcian Blue (AB pH 1.0 and pH 2.5) and AB (pH 2.5) + PAS. The esophagus has longitudinal folds to facilitate the passage of food. The saccular stomach was divided into cardiac regions with longitudinal fo lds, funica that presents folds in different orientations and pyloric with developed musculature characterizing a sphincter. The intestine was short divided into anterior, medium, posterior and rectum. The intestinal folds are transversal and thick, mainly in the anterior region, decreasing in thickness in the aboral direction, increasing the food retention time. The intestine length was 39.8 cm ± 7 and the intestinal coefficient was 1.1. The intestine presented on average 54 pyloric caeca, simple or with two to five branches. Internally the pyloric caecae were observed longitudinal folds, facilitating the entry and exit of food. Brycon amazonicus is an omnivorous species, but its intestinal coefficient 1.1, distensible stomach and short intestine are typical characteristics of carnivorous fish. However, the transverse folds and the large number of pyloric caecae aid in the digestion and absorption of foods that are difficult to digest in your diet. In relation to histology and histochemistry, the esophagus presented a stratified pavement lining epithelium with the presence of epithelial and goblet cells filled with acidic and neutral mucosubstances. The stomach presented a mucous layer formed by the columnar simple lining epithelium with epithelial cells having apical mucosubstances mostly neutral, in addition to being able to observe a well-developed glandular portion in the cardiac and fundal region. The aglandular pyloric region, on the other hand, showed a thick muscular layer (pyloric sphincter). The intestine presented simple columnar lining epithelium with the presence of absorptive cells or enterocytes with a brush border and goblet cells filled with neutral and acidic mucins. The rectum and pyloric cecum showed similar histological and histochemical characteristics to the intestine, but in the rectum region it was possible to observe a great development of the internal muscular layer. Mucosubstances or mucins of an acid and neutral character present in all digestive tract have a general function of prot ection and lubrication of the epithelium.