Alimentary Tract Anatomy and Morphology in Early Adult Mediterranean Killifish Aphanius fasciatus (Valenciennes, 1821)

<b>Background/Aims:</b> The Mediterranean killifish, <i>Aphanius fasciatus</i> (Valenciennes, 1821), is a small euryhaline and eurytherm cyprinodont. While its ecology and role as a bioindicator are well known, its anatomy remains poorly understood. This study aimed to provide the first detailed description of the digestive tract of <i>A. fasciatus</i>, from the oropharyngeal cavity to the rectum. <b>Methods:</b> An anatomical and morphological approach supported by light microscopy was applied to examine oral, pharyngeal, and intestinal structures in adult specimens. <b>Results:</b> The jaws bear tricuspids incisiform teeth, whereas the pharynx has caniniform teeth. The tongue forms a muscular thickening of the oral floor and aids swallowing. The oropharyngeal tract and esophagus lead to a dilated anterior intestinal region resembling a primitive stomach, with mucosal folds and mucus-secreting epithelium, but lacking gastric glands. This chamber functions mainly for food storage, absorption, and preparation rather than true gastric digestion. The intestine extends to the rectum, showing sexual dimorphism: females have a relaxed anus, males a more toned and folded structure. <b>Conclusions:</b> These findings provide essential baseline information for comparison with other experimental models and reinforce the suitability of <i>A. fasciatus</i> as a reliable model for anatomical and functional studies.