Ontogeny of stomach functionality during the larval development of the red porgy was studied from morphological, physiological and molecular perspectives. The aim of this study was to advance our understanding of the sequence of events occurring during the transition from alkaline to acid digestion in sparids. Gastric gland histological development was examined using haematoxylin-eosin staining. Pepsinogen mRNA was localized using in situ hybridization on 5-7 μm sections of paraffin embedded samples. Gastric pH in the lumen of the stomach was measured using a pH microelectrode. The first signs of gastric glands were apparent by 19 days after hatching (dah) and were fully morphologically developed on 26 dah approximately. Pepsinogen expression was evidenced in the gastric glands from 30 dah onwards. The decrease in gastric pH was detected in fed larvae above 35 dah. © 2005 Elsevier B.V. All rights reserved.