Intestinal histomorphology, autochthonous microbiota and growth performance of the oscar ( Astronotus ocellatus Agassiz, 1831) following dietary administration of xylooligosaccharide

Summary The present study investigates the changes in intestinal histomorphology, autochthonous microbiota and growth performance of the oscar, Astronotus ocellatus , following dietary administration of different levels of xylooligosaccharide ( XOS ). One hundred forty‐four oscars (8.88 ± 0.23 g; n = 144) were randomly stocked in 12 aquaria (100‐L) assigned to four treatments repeated in triplicate. Fish were fed a commercial diet, Biomar, supplemented with different levels (0 [control], 0.5, 1, 2%) of XOS for 8 weeks. Treatments were investigated under static aerated water conditions with a 70% daily water exchange. Evaluation of intestinal histomorphology (villus height, enterocytes height and thickness of the tunica muscularis) revealed no significant differences between XOS ‐fed groups and the control treatment (P   >   0.05). However, administration of XOS in the oscar diet increased the total autochthonous intestinal heterotrophic bacteria significantly (P   <   0.05). Autochthonous lactic acid bacteria levels were also significantly elevated in XOS ‐fed groups (P   <   0.05). Furthermore, dietary XOS remarkably increased growth performance (control: 22.76 ± 2.79, 2% XOS : 29.13 ± 2. 8; n = 12) parameters of the oscar (P   <   0.05). These results demonstrated the beneficial effects of XOS on the growth performance and intestinal microbiota of A. ocellatus .