Anatomical and histological adaptations of digestive tract in relation to food and feeding habits of lizardfish, Synodus variegatus (Lacepède, 1803) Ahmed N. Alabssawy a,⇑ , Hassan M.M. Khalaf-Allah a , Ahmed A. Gafar b a Marine science and fishes branch, Zoology Department, Faculty of Science, Al-Azhar University, Cairo, Egypt b Zoology Department, Faculty of Science, Al-Azhar University, Cairo, Egypt article info Article history: Received 6 December 2018 Revised 12 May 2019 Accepted 12 May 2019 Available online xxxx Keywords: Adaptations Alimentary canal Histoarchitecture Lizardfish Morphology abstract The adaptations in anatomical and histological structures of the digestive tract of fish are correlated with their food and feeding habits. An understanding of these habits is essential to emphasize the related func- tional mechanisms of fish digestive physiology. Little is known about the adaptations of the alimentary tract of coral reef fish to food and feeding strategies in the Egyptian Red Sea. The present study investi- gated the anatomical and histological structure of the digestive tract of the lizardfish, Synodus variegatus. The results indicated that the oesophagus in S. variegatus is a short, narrow and distensible muscular tube, that is adapted to conduction of food. The mucosa is composed of a thin stratum of simple columnar epithelium opens to the lumen and a thick layer of mucous tubular glands located at the base in both the anterior and posterior oesophagus. The muscular layer is formed of one circular layer. The stomach has a great distensibility with a bag-like shape to enable the fish to swallow relatively huge preys. Further, it has numerous gastric glands in the cardiac portion for food digestion. As for the pyloric portion, it is a very dense layer of muscularis, which contributes in regulating the passage of digested food to the intes- tine. The relative length of gut ranges from 0.67 to 0.73 cm with an average of 0.7 ± 0.02 cm. The intestine is a short uncomplicated tube. The mucosal folds in the anterior intestine are very long, numerous and with round tips. Such structures are shorter and fewer in number towards the mid intestine, and much thicker and blunt in the posterior intestine. The epithelial lining of the intestine consists of columnar cells for absorption, and numerous large goblet cells for the lubrication of feces. Finally, based on the findings of the anatomical and histological investigations, it may be concluded that there is a correlation between the adaptations in the digestive tract structure of the lizardfish, S. variegatus, and their feeding habits. Ó 2019 Hosting by Elsevier B.V. on behalf of National Institute of Oceanography and Fisheries. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Introduction The adaptations in reef-dwelling fishes suited to particular types of food sources are commonly found in coral reef habitats. Feeding habits among reef fishes have been classified into four basic types of feeders: herbivorous, planktivorous, benthic carniv- orous and piscivorous (Alevizon, 1994; Lieske and Myers, 2004). Lieske and Myers (1999) reported that piscivorous coral reef fish are those that prey mainly or entirely upon other fishes. The predation keeps the populations balanced from reaching levels of competitions among species. There are three different basic hunt- ing strategies employed by such predators, each requiring different physical adaptations and behaviors. Lizardfishes derive their name from their reptile-like heads. Their mouth is large with many rows of tiny teeth. They sit on sed- imentary bottoms, darting upward waiting to seize preys with great rapidity (usually small fishes) that venture near them (Rahimibashar et al., 2012). Generally, the adaptations of the fish digestive organs to their normal diet are especially evident with regard to form, size, struc- ture, abundance and limitation of the microscopic parts, such as dentition, mucous cells, taste buds, digestive glands and muscular coat in the oesophagus, stomach and intestine of the fish. All of these features are subjected to diverse variations and significant modifications, which conform to the food and feeding habits (Dasgupta, 2000; Khalaf-Allah, 2013; Shalaby, 2017). In the stom- ach of piscivorous fish, Tylosurus choram, numerous gastric glands https://doi.org/10.1016/j.ejar.2019.05.006 1687-4285/Ó 2019 Hosting by Elsevier B.V. on behalf of National Institute of Oceanography and Fisheries. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer review under responsibility of National Institute of Oceanography and Fisheries. ⇑ Corresponding author. E-mail address: ahmed_alabssawy@yahoo.com (A.N. Alabssawy). Egyptian Journal of Aquatic Research xxx (xxxx) xxx Contents lists available at ScienceDirect Egyptian Journal of Aquatic Research journal homepage: www.sciencedirect.com/locate/ejar Please cite this article as: A. N. Alabssawy, H. M. M. Khalaf-Allah and A. A. Gafar, Anatomical and histological adaptations of digestive tract in relation to food and feeding habits of lizardfish, Synodus variegatus (Lacepède, 1803), Egyptian Journal of Aquatic Research, https://doi.org/10.1016/j.ejar.2019.05.006