Abstract
Simple SummaryNutritional strategies focused on the use of botanicals as modulators of several physiological responses and health promoters of the gastrointestinal tract have attracted interest in animal production. Previous research indicates the positive results of using essential oils (EOs) as natural feed additives for several farmed animals. In the last decades, these nutritional alternatives have been evaluated and reported in fish production in order to increase fish growth and feed utilization and to promote animal welfare. Therefore, the present study was designed to compare the effects of feed EO supplementation in two different forms (natural and composed of active ingredients obtained by synthesis) on the gastric mucosa in European sea bass. EOs decrease oxyntopeptic cells and increase somatostatin and ghrelin enteroendocrine cells. In addition, we showed that Na+K+-ATPase was expressed in oxyntopeptic cells (OPs) in the same way as H+K+-ATPase (typical marker for mammalian parietal cells) and, for this reason, consider Na+K+-ATPase a valid marker for OPs.The current work was designed to assess the effect of feed supplemented with essential oils (EOs) on the histological features in sea bass’s gastric mucosa. Fish were fed three diets: control diet (CTR), HERBAL MIX® made with natural EOs (N-EOs), or HERBAL MIX® made with artificial EOs obtained by synthesis (S-EOs) during a 117-day feeding trial. Thereafter, the oxyntopeptic cells (OPs) and the ghrelin (GHR) and somatostatin (SOM) enteroendocrine cells (EECs) in the gastric mucosa were evaluated. The Na+K+-ATPase antibody was used to label OPs, while, for the EECs, anti-SOM and anti-GHR antibody were used. The highest density of OP immunoreactive (IR) area was in the CTR group (0.66 mm2 ± 0.1). The OP-IR area was reduced in the N-EO diet group (0.22 mm2 ± 1; CTR vs. N-EOs, p < 0.005), while in the S-EO diet group (0.39 mm2 ± 1) a trend was observed. We observed an increase of the number of SOM-IR cells in the N-EO diet (15.6 ± 4.2) compared to that in the CTR (11.8 ± 3.7) (N-EOs vs. CTR; p < 0.05), but not in the S-EOs diet. These observations will provide a basis to advance current knowledge on the anatomy and digestive physiology of this species in relation to pro-heath feeds.
Highlights
In the last decade, the application of natural feed additives has been able to support optimal gut health and function, enhancing growth, feed utilization, and disease prevention in the whole aquaculture sector [1,2]
N-Essential oils (EOs) contained a blend of natural essential oils of thyme, garlic, rosemary, and cinnamon, while S-EOs was a blend of thymol and carvacrol, diallyl sulfide, cineol, and cinnamaldehyde
No significant differences were observed in final body weight, SGR, feed conversion rate (FCR), and feed intake (FI) during the overall trial (p < 0.05)
Summary
The application of natural feed additives has been able to support optimal gut health and function, enhancing growth, feed utilization, and disease prevention in the whole aquaculture sector [1,2]. Essential oils (EOs) are extracted from plants raw materials and contain compounds produced during plant secondary metabolism. They are natural multicomponent systems of volatile, lipophilic, odoriferous, and liquid substances, obtained from complex mixtures of low-molecular-weight substances [3,4]. EOs have been the focus of aquaculture studies due to their diverse properties, and they are good candidates as they enhance the health, growth, and welfare of the fish [3]. In no-mammalian vertebrates, one cell type, the oxyntopeptic cells (OPs), secretes both hydrochloric acid and pepsinogen into the lumen to initiate protein digestion [7,8,9,10]
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