Abstract
Geophagus brasiliensis, popularly known as acará, is a common fish in lentic freshwater environments in South America. This species has a detritivorous-iliophagous or omnivorous feeding habit, with high food plasticity; however, there are no studies describing its intestinal tract histologically. Therefore, the present study analysed through histological and histochemical techniques the intestines of the acará. Adult specimens were collected with gillnets, anaesthetized and euthanized. Then, the fish were submitted to biometry and dissection to remove fragments of intestines. The samples were fixed in Bouin liquid for 12 hours and subjected to histological and histochemical techniques. Histologically, all samples of intestines were organized into four layers: mucosa, submucosa, muscular and serosa. The small intestine (foregut and midgut) was characterized by the presence of intestinal villi covered by simple prismatic epithelium with a striated border and goblet cells supported by the connective lamina propria. In the large intestine (hindgut), there was an absence of villi and an abundance of goblet cells. Positive reaction to Periodic Acid–Schiff (PAS) and Alcian Blue (AB) pH 2.5 reactions were detected in goblet cells, indicating the presence of mucosubstances. No lipids were detected in the intestine cells due to the negative reaction to the Sudan Black B. The results of the present study provide subsidies for a better understanding of the intestinal morphology of teleosts and provide valuable information for phylogenetic studies.
KEYWORDS: enterocytes, goblet cells, lymphocytes, mucosubstances, teleosts
INTRODUCTION
The digestive system of fish presents marked morphological and functional variations, which reflect the wide diversity of this group and its different feeding habits (Díaz, García, Devincenti, & Goldemberg, 2003). The general morphology of the digestive tract is mainly related to the nature of the feeding habits, the environment in which the fish inhabit, and the size and shape of the body (Andrade, Guimarães, Rotundo & Mari, 2017). In teleosts, it has some basic structural similarities, such as its anatomical division, consisting of the buccopharyngeal cavity, oesophagus, stomach, intestines, anus and accessory organs such as the liver, gallbladder and pancreas (Santos, Arantes, Santiago & Santos, 2015). However, depending on the feeding habit, the gastrointestinal tract can vary between species. For example, the size of the stomach and intestines, the presence of pyloric cecum in the intestines and the content of secretion produced by some cells (Baldisserotto et al., 2014).
The small intestine, also subdivided in foregut and mid gut, is a tubular organ in which food transits and is responsible for alkaline digestion, absorption of nutrients, water and electrolytes, and help the immune system (Nachi et al., 1998). This section of the gastrointestinal tract contains specialized structures such as villi, microvilli and pyloric cecum that increase the absorption area (Santos et al., 2015). The presence of longitudinal folds, and the inner circular and outer longitudinal muscle layers, together promote a peristaltic activitythat facilitates the transit of food ( Genten et al., 2009).
The large intestine, also called hindgut, located in the caudal region does not present villi and is related to the absorption of water and electrolytes, mucus secretion and faeces elimination. This section presents specializations such as intestinal absorptive cells and numerous goblet cells (Amorim et al., 2009).
Geophagus brasiliensis (Quoy & Gaimard, 1824), popularly known as acará, cará or papa-terra, belongs to the order Cichliformes. It is widely distributed in lentic environments of coastal watersheds in Uruguay and eastern and southeastern Brazil (Buckup et al., 2007; Graça & Pavanelli, 2007; Meschiatti, 1995; Reis et al., 2003). Acará is a territorial species, found in backwaters, close to the bottom, presenting daytime activity, visual guidance and parental care, including storing eggs in a nest or substrate (Barlow, 2000). This species has a great potential for ornamental aquaculture due to its ease of reproduction in captivity, attractive colour and behaviour (Assis et al., 2014; Bizerril & da Silveira Primo, 2001).
The acará has a high degree of food plasticity and has been described at different trophic levels, which reflects its ability to adapt and survive in different environments (Abelha & Goulart, 2004; Bastos et al., 2011; Nunes et al., 2014). Some authors describe its feeding habits as omnivorous, with a high incidence of insects and microcrustaceans (Sabino & Castro, 1990; Stefani, 2006). Others define this species as detritivorous-iliophagous (Meschiatti, 1995). According to Lazzaro (1991), specimens with less than 4.0 cm in size feed mainly on insect larvae, while specimens longer than 4.0 cm have a more diversified diet, with the main foods being insects and gastropods. Other foods are arthropod fragments, plant fragments,
sediments, algae and other items (Azevedo et al., 2006).
Due to its ecological and economical importance, and the lack of studies on the gastrointestinal description of Geophagus brasiliensis, this study aims to describe the intestines of this species using histological, histochemical and histometric techniques, generating important data for phylogenetic studies and the conservation of the species.
MATERIALS AND METHODS
Sampling
The sampling occurred between October and December 2019 in a small lake from the Sao Francisco River basin. Forty (n = 40) adult fish were collected (20 males and 20 females). The fish were anaesthetized with Eugenol (30 mg/L) and euthanized by the cross section of the cervical medulla following the ethical principles established by the National Council for the Control of Animal Experiments (CONCEA, 2013). The specimens were transported to the Ichthyology Laboratory of the Postgraduate Program in Vertebrate Biology at PUC Minas, where biometrics and dissection of specimens were performed. The research was approved by the Ethics Committee on the Use of Animals (CEUA PUC Minas protocol No. 26/2019).
Acesse o artigo completo gratuitamente:
