RESEARCH ARTICLE Copyright © 2017 American Scientific Publishers All rights reserved Printed in the United States of America Journal of Advanced Microscopy Research Vol. 12, 1–5, 2017 Histology, Histochemistery and Surface Architecture of the Rectum of Grass Carp (Ctenopharyngodon idella) Doaa M. Mokhtar ∗ , Enas A. Abd-Elhafez, and Ahmed H. S. Hassan Department of Anatomy and Histology, Faculty of Vet. Medicine, Assuit University, 71526, Egypt The rectum of grass carp was characterized by presence of mucosal wavy folds and a large diam- eter of its lumen, which may act as temporary storage part for excretory materials. Also, the mus- cularis layer showed a thick-walled as compared with the anterior and posterior portions of the intestine, which would contribute to the expulsion of faecal materials to the anus. Semithin sections of rectal epithelium revealed presence of small vesicles in the enterocytes that indicated its absorp- tive role, which was confirmed by presence of microvilli and increase in height of the epithelium. On the other hand, the rectum was characterized by an increase in number of goblet cells that reacted intensely with PAS, alcian blue and toluidine blue that may respond to an increased need of lubrication required for expulsion of faeces and protection of mucosa. Keywords: Rectum, Absorptive Epithelium, Goblet Cells, SEM. 1. INTRODUCTION The intestine is an organ, which is involved in various important physiological functions. According to previous studies, intestinal morphology and histology of fish diges- tive tract is influenced by feeding behavior, food intake regularity a well as body size and shape. 1–3 The histology and histochemistry of the mucous layer have been studied in some fishes like flower fish (Pseudo- phoxinus antalyee), rice field ell (Monopoterus albus), white sturgeons (Asipensor transmontanus) and Dover sole (Solea solea). In these fishes, goblet cells and epithelium of the intestinal layer are the main mucous secreting cells of the intestine. 4 5 But variation can be seen in the struc- ture and arrangement of cells in different of cells in dif- ferent species. The grass carp or white amur (Ctenopharyngodon idella) is a cyprinid fish characterized by herbivorous feed- ing manner that it usually feeds on grasses or other aquatic vegetations and can be grown together with other fish species. 6 The purpose of this study is to describe the structure of the rectum of Ctenopharyngodon idella using light microscopy, histochemistry as well as the scanning elec- tron microscopy. 2. MATERIALS AND METHODS This study was conducted in accordance with the Egyptian laws and University guidelines for the care of experimental ∗ Author to whom correspondence should be addressed. animals. All procedures of the current study have been approved by the Committee of Faculty of Veterinary Medicine, Assiut University, Egypt. 2.1. Source of Samples The materials employed in this study consisted of ran- domly obtained 20 adult specimens of both sex of the grass carp (Ctenopharyngodon idella). The materials were col- lected from fish farm in El-Minea during the year. The specimens were 37.20 ± 4.0 cm in standard length and 421.60 ± 8.70 gm in body weight. 2.2. Histological Analysis The samples for histological examination were dissected as soon as possible from rectum of grass carp through a middle incision in the abdominal cavity. All samples were dissected at 1 × 1 × 0.5 cm and were immediately fixed in Bouin’s fluid for 22 hours. The fixed materials were dehy- drated in an ascending series of ethanol, cleared in methyl benzoate and then embedded in paraffin wax. Transverse and longitudinal paraffin sections at 5–8 m in thick- ness were cut and stained with Harris haematoxylin and Eosin for general histological examination, Crossmon’s trichrome for collagen fibers and smooth muscle cells. 7 2.3. Histochemical Analysis Representative sections were stained with PAS for detec- tion of neutral mucins and combined alcian blue-PAS tech- nique for acid and neutral mucins. 7 J. Adv. Microsc. Res. 2017, Vol. 12, No. 2 2156-7573/2017/12/001/005 doi:10.1166/jamr.2017.1332 1