Abstract
This study aimed to evaluate the effect of oregano oil on the intestinal and liver morphometry of yellow tail tetra, Astyanax altiparanae. Fish (1.46 ± 0.09 g) were kept in a 60-L aquaria, at a stocking density of 0.5 fi sh L-1. Six diets containing varying amounts of oregano oil were evaluated (0.0; 0.5; 1.0; 1.5; 2.0 and 2.5 g of oregano oil kg-1). At the end of 90 days, the fi sh were euthanised. Four intestines and four livers were collected per treatment, which were fi xed in Bouin and embedded in resin. For height and width folds, the absorption surface area and thickness of the muscular layer a positive linear effect of oregano oil was observed. A decrescent linear effect on the total number of goblet cells was also observed. For the cytoplasmic percentage of hepatocytes and liver glycogen, a positive linear effect of oregano oil was observed. There was a decreasing linear effect on the percentage of nuclei in the hepatocytes and capillaries. Thus, the oregano essential oil promotes increased absorption areas, modulates the amount of goblet cells involved in protecting the intestinal mucosa and promotes cytoplasmic increase with greater deposition of liver glycogen in yellow tail tetra.
Highlights
Knowledge of gut histology and the digestion and absorption processes of nutrients is essential for understanding fish physiology and nutrition
For the fold height (FH), fold width (FW), absorption surface area (ASA) and the muscle layer thickness (MLT), there was a linear effect for the oregano oil (Table I, Fig. 2)
The increased height, width and absorption surface area of the folds may be related to the antimicrobial activity of oregano oil (Burt and Reinders 2003, Sartoratto et al 2004, Souza et al 2006, Oliveira et al 2009, Cleff et al 2010), causing a reduction of unwanted bacteria (Kirkpinar et al 2011, Giannenas et al 2012) and a consequent reduction of mucosal damage
Summary
Knowledge of gut histology and the digestion and absorption processes of nutrients is essential for understanding fish physiology and nutrition This knowledge can contribute to the formulation of fish diets and the feeding management for these animals, resulting in increased productivity and reduced production costs (Castro et al 2002, Faccioli et al 2014). Essential oils stand out among the growth promoters because they are natural products with good availability, they have fewer side effects, lower levels of toxicity, and better biodegradability. These characteristics make them safe in terms of animal and human health, in addition to being safer for the environment (Kalemba and Kunicka 2003). Possible ways that essential oils affect the body of animals include: 1) controlling pathogens due to the oil’s antimicrobial activity (Rao et al 2006, Sahu et al 2007, Aly and Mohamed 2010); 2) the antioxidant activity related to the presence of phenolic compounds, flavonoids and terpenoids (Zheng et al 2009); 3) improving digestion by stimulating the secretion of digestive enzymes (Lee et al 2004); and 4) improving absorption capacity of nutrients due to their beneficial effects on the height villus and depth crypt of the intestinal epithelium (Petrolli et al 2012, Zanini et al 2012)
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